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 $83.41   12.728%   $94.0264   $94.03   $94.05   $94.00  
  Purchase #2 $125.26   10.640%   $138.5877   $138.59   $138.60   $138.60  
  Purchase #3 $173.98   8.522%   $188.8066   $188.81   $188.80   $188.80  
  Purchase #4 $189.85   6.416%   $202.0308   $202.03   $202.05   $202.00  
  Purchase #5 $48.82   9.425%   $53.4213   $53.42   $53.40   $53.40  
  Purchase #6 $125.57   11.175%   $139.6024   $139.60   $139.60   $139.60  
  Purchase #7 $60.53   10.255%   $66.7374   $66.74   $66.75   $66.70  
  7 purchase totals = $807.42       $883.2126   $883.22   $883.25   $883.10