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 $48.42   12.419%   $54.4333   $54.43   $54.45   $54.40  
  Purchase #2 $213.95   12.490%   $240.6724   $240.67   $240.65   $240.70  
  Purchase #3 $64.29   5.228%   $67.6511   $67.65   $67.65   $67.70  
  Purchase #4 $178.47   10.744%   $197.6448   $197.64   $197.65   $197.60  
  Purchase #5 $59.27   5.452%   $62.5014   $62.50   $62.50   $62.50  
  Purchase #6 $179.40   4.686%   $187.8067   $187.81   $187.80   $187.80  
  Purchase #7 $84.42   9.326%   $92.293   $92.29   $92.30   $92.30  
  7 purchase totals = $828.22       $903.0027   $902.99   $903.00   $903.00