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 $48.50   9.211%   $52.9673   $52.97   $52.95   $53.00  
  Purchase #2 $32.36   3.541%   $33.5059   $33.51   $33.50   $33.50  
  Purchase #3 $224.76   7.748%   $242.1744   $242.17   $242.15   $242.20  
  Purchase #4 $55.50   3.139%   $57.2421   $57.24   $57.25   $57.20  
  Purchase #5 $209.87   12.570%   $236.2507   $236.25   $236.25   $236.30  
  Purchase #6 $105.92   11.541%   $118.1442   $118.14   $118.15   $118.10  
  Purchase #7 $249.70   5.415%   $263.2213   $263.22   $263.20   $263.20  
  7 purchase totals = $926.61       $1,003.5059   $1,003.50   $1,003.45   $1,003.50