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 $84.60   10.864%   $93.7909   $93.79   $93.80   $93.80  
  Purchase #2 $209.43   5.492%   $220.9319   $220.93   $220.95   $220.90  
  Purchase #3 $31.36   3.869%   $32.5733   $32.57   $32.55   $32.60  
  Purchase #4 $245.55   4.555%   $256.7348   $256.73   $256.75   $256.70  
  Purchase #5 $142.72   12.824%   $161.0224   $161.02   $161.00   $161.00  
  Purchase #6 $125.66   3.282%   $129.7842   $129.78   $129.80   $129.80  
  Purchase #7 $63.60   7.247%   $68.2091   $68.21   $68.20   $68.20  
  7 purchase totals = $902.92       $963.0466   $963.03   $963.05   $963.00