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 $92.66   12.436%   $104.1832   $104.18   $104.20   $104.20  
  Purchase #2 $244.35   5.662%   $258.1851   $258.19   $258.20   $258.20  
  Purchase #3 $52.43   12.386%   $58.924   $58.92   $58.90   $58.90  
  Purchase #4 $185.38   11.652%   $206.9805   $206.98   $207.00   $207.00  
  Purchase #5 $75.64   12.769%   $85.2985   $85.30   $85.30   $85.30  
  Purchase #6 $173.29   3.452%   $179.272   $179.27   $179.25   $179.30  
  Purchase #7 $125.85   9.665%   $138.0134   $138.01   $138.00   $138.00  
  7 purchase totals = $949.60       $1,030.8567   $1,030.85   $1,030.85   $1,030.90