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 $81.35   13.594%   $92.4087   $92.41   $92.40   $92.40  
  Purchase #2 $125.86   6.874%   $134.5116   $134.51   $134.50   $134.50  
  Purchase #3 $244.58   12.644%   $275.5047   $275.50   $275.50   $275.50  
  Purchase #4 $59.80   11.539%   $66.7003   $66.70   $66.70   $66.70  
  Purchase #5 $19.88   3.769%   $20.6293   $20.63   $20.65   $20.60  
  Purchase #6 $217.55   8.279%   $235.561   $235.56   $235.55   $235.60  
  Purchase #7 $154.74   5.307%   $162.9521   $162.95   $162.95   $163.00  
  7 purchase totals = $903.76       $988.2677   $988.26   $988.25   $988.30