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 $51.52   12.487%   $57.9533   $57.95   $57.95   $58.00  
  Purchase #2 $29.74   9.633%   $32.6049   $32.60   $32.60   $32.60  
  Purchase #3 $144.41   8.709%   $156.9867   $156.99   $157.00   $157.00  
  Purchase #4 $118.68   10.690%   $131.3669   $131.37   $131.35   $131.40  
  Purchase #5 $199.94   3.386%   $206.71   $206.71   $206.70   $206.70  
  Purchase #6 $241.46   13.527%   $274.1223   $274.12   $274.10   $274.10  
  Purchase #7 $63.62   13.645%   $72.3009   $72.30   $72.30   $72.30  
  7 purchase totals = $849.37       $932.0450   $932.04   $932.00   $932.10