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 $41.95   12.533%   $47.2076   $47.21   $47.20   $47.20  
  Purchase #2 $52.33   12.735%   $58.9942   $58.99   $59.00   $59.00  
  Purchase #3 $71.25   10.190%   $78.5104   $78.51   $78.50   $78.50  
  Purchase #4 $247.29   6.282%   $262.8248   $262.82   $262.80   $262.80  
  Purchase #5 $70.60   8.156%   $76.3581   $76.36   $76.35   $76.40  
  Purchase #6 $59.48   7.600%   $64.0005   $64.00   $64.00   $64.00  
  Purchase #7 $230.92   3.381%   $238.7274   $238.73   $238.75   $238.70  
  7 purchase totals = $773.82       $826.6230   $826.62   $826.60   $826.60