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 $241.93   13.813%   $275.3478   $275.35   $275.35   $275.30  
  Purchase #2 $198.69   13.483%   $225.4794   $225.48   $225.50   $225.50  
  Purchase #3 $50.60   12.624%   $56.9877   $56.99   $57.00   $57.00  
  Purchase #4 $125.67   3.117%   $129.5871   $129.59   $129.60   $129.60  
  Purchase #5 $6.56   5.838%   $6.943   $6.94   $6.95   $6.90  
  Purchase #6 $110.90   8.697%   $120.545   $120.55   $120.55   $120.50  
  Purchase #7 $150.66   10.533%   $166.529   $166.53   $166.55   $166.50  
  7 purchase totals = $885.01       $981.4190   $981.43   $981.50   $981.30