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 $24.82   5.148%   $26.0977   $26.10   $26.10   $26.10  
  Purchase #2 $205.30   9.213%   $224.2143   $224.21   $224.20   $224.20  
  Purchase #3 $112.56   11.787%   $125.8274   $125.83   $125.85   $125.80  
  Purchase #4 $36.30   9.162%   $39.6258   $39.63   $39.65   $39.60  
  Purchase #5 $70.43   4.157%   $73.3578   $73.36   $73.35   $73.40  
  Purchase #6 $85.69   6.168%   $90.9754   $90.98   $91.00   $91.00  
  Purchase #7 $175.39   4.783%   $183.7789   $183.78   $183.80   $183.80  
  7 purchase totals = $710.49       $763.8773   $763.89   $763.95   $763.90