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 $48.77   8.636%   $52.9818   $52.98   $53.00   $53.00  
  Purchase #2 $64.73   6.491%   $68.9316   $68.93   $68.95   $68.90  
  Purchase #3 $191.80   8.215%   $207.5564   $207.56   $207.55   $207.60  
  Purchase #4 $50.49   7.382%   $54.2172   $54.22   $54.20   $54.20  
  Purchase #5 $190.33   8.249%   $206.0303   $206.03   $206.05   $206.00  
  Purchase #6 $140.33   12.503%   $157.8755   $157.88   $157.90   $157.90  
  Purchase #7 $7.78   7.250%   $8.3441   $8.34   $8.35   $8.30  
  7 purchase totals = $694.23       $755.9369   $755.94   $756.00   $755.90