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 $162.67   12.844%   $183.5633   $183.56   $183.55   $183.60  
  Purchase #2 $101.49   6.333%   $107.9174   $107.92   $107.90   $107.90  
  Purchase #3 $144.28   10.455%   $159.3645   $159.36   $159.35   $159.40  
  Purchase #4 $16.71   5.517%   $17.6319   $17.63   $17.65   $17.60  
  Purchase #5 $55.29   6.290%   $58.7677   $58.77   $58.75   $58.80  
  Purchase #6 $70.93   4.638%   $74.2197   $74.22   $74.20   $74.20  
  Purchase #7 $179.94   8.435%   $195.1179   $195.12   $195.10   $195.10  
  7 purchase totals = $731.31       $796.5824   $796.58   $796.50   $796.60