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 $245.85   10.391%   $271.3963   $271.40   $271.40   $271.40  
  Purchase #2 $214.66   8.804%   $233.5587   $233.56   $233.55   $233.60  
  Purchase #3 $44.56   8.243%   $48.2331   $48.23   $48.25   $48.20  
  Purchase #4 $118.98   6.394%   $126.5876   $126.59   $126.60   $126.60  
  Purchase #5 $66.65   13.629%   $75.7337   $75.73   $75.75   $75.70  
  Purchase #6 $98.55   13.552%   $111.9055   $111.91   $111.90   $111.90  
  Purchase #7 $82.61   10.401%   $91.2023   $91.20   $91.20   $91.20  
  7 purchase totals = $871.86       $958.6172   $958.62   $958.65   $958.60