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 $85.65   10.109%   $94.3084   $94.31   $94.30   $94.30  
  Purchase #2 $232.82   4.172%   $242.5333   $242.53   $242.55   $242.50  
  Purchase #3 $35.99   3.803%   $37.3587   $37.36   $37.35   $37.40  
  Purchase #4 $189.99   12.460%   $213.6628   $213.66   $213.65   $213.70  
  Purchase #5 $162.72   3.637%   $168.6381   $168.64   $168.65   $168.60  
  Purchase #6 $116.29   13.315%   $131.774   $131.77   $131.75   $131.80  
  Purchase #7 $68.79   8.770%   $74.8229   $74.82   $74.80   $74.80  
  7 purchase totals = $892.25       $963.0982   $963.09   $963.05   $963.10