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 $47.67   13.236%   $53.9796   $53.98   $54.00   $54.00  
  Purchase #2 $94.29   6.529%   $100.4462   $100.45   $100.45   $100.40  
  Purchase #3 $188.97   13.191%   $213.897   $213.90   $213.90   $213.90  
  Purchase #4 $232.86   8.198%   $251.9499   $251.95   $251.95   $251.90  
  Purchase #5 $102.35   12.361%   $115.0015   $115.00   $115.00   $115.00  
  Purchase #6 $179.49   9.518%   $196.5739   $196.57   $196.55   $196.60  
  Purchase #7 $29.96   7.684%   $32.2621   $32.26   $32.25   $32.30  
  7 purchase totals = $875.59       $964.1102   $964.11   $964.10   $964.10