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 $64.43   6.636%   $68.7056   $68.71   $68.70   $68.70  
  Purchase #2 $222.53   9.491%   $243.6503   $243.65   $243.65   $243.70  
  Purchase #3 $149.96   5.831%   $158.7042   $158.70   $158.70   $158.70  
  Purchase #4 $97.96   4.128%   $102.0038   $102.00   $102.00   $102.00  
  Purchase #5 $212.55   11.316%   $236.6022   $236.60   $236.60   $236.60  
  Purchase #6 $28.59   4.329%   $29.8277   $29.83   $29.85   $29.80  
  Purchase #7 $32.84   6.800%   $35.0731   $35.07   $35.05   $35.10  
  7 purchase totals = $808.86       $874.5669   $874.56   $874.55   $874.60