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 $65.96   13.621%   $74.9444   $74.94   $74.95   $74.90  
  Purchase #2 $32.53   12.302%   $36.5318   $36.53   $36.55   $36.50  
  Purchase #3 $97.47   7.308%   $104.5931   $104.59   $104.60   $104.60  
  Purchase #4 $215.93   4.475%   $225.5929   $225.59   $225.60   $225.60  
  Purchase #5 $131.43   13.533%   $149.2164   $149.22   $149.20   $149.20  
  Purchase #6 $214.62   6.417%   $228.3922   $228.39   $228.40   $228.40  
  Purchase #7 $167.42   6.312%   $177.9876   $177.99   $178.00   $178.00  
  7 purchase totals = $925.36       $997.2584   $997.25   $997.30   $997.20