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 $218.93   13.215%   $247.8616   $247.86   $247.85   $247.90  
  Purchase #2 $56.49   5.806%   $59.7698   $59.77   $59.75   $59.80  
  Purchase #3 $116.82   3.681%   $121.1201   $121.12   $121.10   $121.10  
  Purchase #4 $196.95   5.518%   $207.8177   $207.82   $207.80   $207.80  
  Purchase #5 $53.53   7.233%   $57.4018   $57.40   $57.40   $57.40  
  Purchase #6 $150.56   12.369%   $169.1828   $169.18   $169.20   $169.20  
  Purchase #7 $11.30   9.272%   $12.3477   $12.35   $12.35   $12.30  
  7 purchase totals = $804.58       $875.5015   $875.50   $875.45   $875.50