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 $53.30   12.572%   $60.0009   $60.00   $60.00   $60.00  
  Purchase #2 $207.49   5.145%   $218.1654   $218.17   $218.15   $218.20  
  Purchase #3 $59.86   3.747%   $62.103   $62.10   $62.10   $62.10  
  Purchase #4 $143.59   8.551%   $155.8684   $155.87   $155.85   $155.90  
  Purchase #5 $200.29   10.105%   $220.5293   $220.53   $220.55   $220.50  
  Purchase #6 $110.49   3.620%   $114.4897   $114.49   $114.50   $114.50  
  Purchase #7 $120.59   10.782%   $133.592   $133.59   $133.60   $133.60  
  7 purchase totals = $895.61       $964.7487   $964.75   $964.75   $964.80