Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $234.29   13.250%   $265.3334   $265.33   $265.35   $265.30  
  Purchase #2 $175.74   12.604%   $197.8903   $197.89   $197.90   $197.90  
  Purchase #3 $214.82   11.137%   $238.7445   $238.74   $238.75   $238.70  
  Purchase #4 $232.89   12.701%   $262.4694   $262.47   $262.45   $262.50  
  Purchase #5 $146.87   6.808%   $156.8689   $156.87   $156.85   $156.90  
  Purchase #6 $157.73   13.724%   $179.3769   $179.38   $179.40   $179.40  
  Purchase #7 $245.33   9.769%   $269.2963   $269.30   $269.30   $269.30  
  7 purchase totals = $1,407.67       $1,569.9797   $1,569.98   $1,570.00   $1,570.00