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 $104.44   13.227%   $118.2543   $118.25   $118.25   $118.30  
  Purchase #2 $213.31   10.283%   $235.2447   $235.24   $235.25   $235.20  
  Purchase #3 $60.77   6.142%   $64.5025   $64.50   $64.50   $64.50  
  Purchase #4 $229.64   5.427%   $242.1026   $242.10   $242.10   $242.10  
  Purchase #5 $11.66   5.842%   $12.3412   $12.34   $12.35   $12.30  
  Purchase #6 $51.96   6.311%   $55.2392   $55.24   $55.25   $55.20  
  Purchase #7 $95.44   4.317%   $99.5601   $99.56   $99.55   $99.60  
  7 purchase totals = $767.22       $827.2446   $827.23   $827.25   $827.20