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 $229.92   10.257%   $253.5029   $253.50   $253.50   $253.50  
  Purchase #2 $175.35   11.623%   $195.7309   $195.73   $195.75   $195.70  
  Purchase #3 $144.84   7.223%   $155.3018   $155.30   $155.30   $155.30  
  Purchase #4 $13.87   6.534%   $14.7763   $14.78   $14.80   $14.80  
  Purchase #5 $169.54   11.159%   $188.459   $188.46   $188.45   $188.50  
  Purchase #6 $56.37   7.745%   $60.7359   $60.74   $60.75   $60.70  
  Purchase #7 $137.47   7.505%   $147.7871   $147.79   $147.80   $147.80  
  7 purchase totals = $927.36       $1,016.2939   $1,016.30   $1,016.35   $1,016.30