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 $59.94   3.788%   $62.2105   $62.21   $62.20   $62.20  
  Purchase #2 $190.25   6.734%   $203.0614   $203.06   $203.05   $203.10  
  Purchase #3 $247.68   6.732%   $264.3538   $264.35   $264.35   $264.40  
  Purchase #4 $87.78   3.856%   $91.1648   $91.16   $91.15   $91.20  
  Purchase #5 $65.79   5.403%   $69.3446   $69.34   $69.35   $69.30  
  Purchase #6 $170.32   10.567%   $188.3177   $188.32   $188.30   $188.30  
  Purchase #7 $130.28   11.188%   $144.8557   $144.86   $144.85   $144.90  
  7 purchase totals = $952.04       $1,023.3085   $1,023.30   $1,023.25   $1,023.40