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 $208.34   12.193%   $233.7429   $233.74   $233.75   $233.70  
  Purchase #2 $126.91   4.542%   $132.6743   $132.67   $132.65   $132.70  
  Purchase #3 $182.52   8.293%   $197.6564   $197.66   $197.65   $197.70  
  Purchase #4 $93.41   7.628%   $100.5353   $100.54   $100.55   $100.50  
  Purchase #5 $168.77   12.842%   $190.4434   $190.44   $190.45   $190.40  
  Purchase #6 $205.46   13.348%   $232.8848   $232.88   $232.90   $232.90  
  Purchase #7 $194.61   9.321%   $212.7496   $212.75   $212.75   $212.70  
  7 purchase totals = $1,180.02       $1,300.6867   $1,300.68   $1,300.70   $1,300.60