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 $91.53   6.683%   $97.6469   $97.65   $97.65   $97.60  
  Purchase #2 $32.61   4.265%   $34.0008   $34.00   $34.00   $34.00  
  Purchase #3 $98.80   7.125%   $105.8395   $105.84   $105.85   $105.80  
  Purchase #4 $188.71   8.341%   $204.4503   $204.45   $204.45   $204.50  
  Purchase #5 $200.97   5.862%   $212.7509   $212.75   $212.75   $212.80  
  Purchase #6 $178.53   10.146%   $196.6437   $196.64   $196.65   $196.60  
  Purchase #7 $77.55   5.763%   $82.0192   $82.02   $82.00   $82.00  
  7 purchase totals = $868.70       $933.3513   $933.35   $933.35   $933.30