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 $245.67   8.706%   $267.058   $267.06   $267.05   $267.10  
  Purchase #2 $207.92   4.621%   $217.528   $217.53   $217.55   $217.50  
  Purchase #3 $6.31   7.734%   $6.798   $6.80   $6.80   $6.80  
  Purchase #4 $92.62   3.193%   $95.5774   $95.58   $95.60   $95.60  
  Purchase #5 $28.47   4.699%   $29.8078   $29.81   $29.80   $29.80  
  Purchase #6 $61.29   5.348%   $64.5678   $64.57   $64.55   $64.60  
  Purchase #7 $209.68   8.823%   $228.1801   $228.18   $228.20   $228.20  
  7 purchase totals = $851.96       $909.5171   $909.53   $909.55   $909.60