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 $245.92   6.658%   $262.2934   $262.29   $262.30   $262.30  
  Purchase #2 $242.71   6.831%   $259.2895   $259.29   $259.30   $259.30  
  Purchase #3 $155.90   6.793%   $166.4903   $166.49   $166.50   $166.50  
  Purchase #4 $41.73   12.564%   $46.973   $46.97   $46.95   $47.00  
  Purchase #5 $179.39   5.701%   $189.617   $189.62   $189.60   $189.60  
  Purchase #6 $118.89   13.117%   $134.4848   $134.48   $134.50   $134.50  
  Purchase #7 $243.71   12.445%   $274.0397   $274.04   $274.05   $274.00  
  7 purchase totals = $1,228.25       $1,333.1877   $1,333.18   $1,333.20   $1,333.20