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 $46.33   12.308%   $52.0323   $52.03   $52.05   $52.00  
  Purchase #2 $118.96   11.829%   $133.0318   $133.03   $133.05   $133.00  
  Purchase #3 $188.34   12.155%   $211.2327   $211.23   $211.25   $211.20  
  Purchase #4 $236.75   5.289%   $249.2717   $249.27   $249.25   $249.30  
  Purchase #5 $51.68   5.681%   $54.6159   $54.62   $54.60   $54.60  
  Purchase #6 $224.26   7.800%   $241.7523   $241.75   $241.75   $241.80  
  Purchase #7 $8.68   11.502%   $9.6784   $9.68   $9.70   $9.70  
  7 purchase totals = $875.00       $951.6151   $951.61   $951.65   $951.60