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 $235.49   10.811%   $260.9488   $260.95   $260.95   $260.90  
  Purchase #2 $35.34   6.192%   $37.5283   $37.53   $37.55   $37.50  
  Purchase #3 $145.59   3.324%   $150.4294   $150.43   $150.45   $150.40  
  Purchase #4 $24.75   6.207%   $26.2862   $26.29   $26.30   $26.30  
  Purchase #5 $47.86   7.166%   $51.2896   $51.29   $51.30   $51.30  
  Purchase #6 $182.68   13.208%   $206.8084   $206.81   $206.80   $206.80  
  Purchase #7 $16.85   3.176%   $17.3852   $17.39   $17.40   $17.40  
  7 purchase totals = $688.56       $750.6759   $750.69   $750.75   $750.60