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 $207.97   7.817%   $224.227   $224.23   $224.25   $224.20  
  Purchase #2 $231.83   13.115%   $262.2345   $262.23   $262.25   $262.20  
  Purchase #3 $74.32   12.230%   $83.4093   $83.41   $83.40   $83.40  
  Purchase #4 $131.94   11.260%   $146.7964   $146.80   $146.80   $146.80  
  Purchase #5 $167.48   10.412%   $184.918   $184.92   $184.90   $184.90  
  Purchase #6 $207.77   13.266%   $235.3328   $235.33   $235.35   $235.30  
  Purchase #7 $136.76   5.136%   $143.784   $143.78   $143.80   $143.80  
  7 purchase totals = $1,158.07       $1,280.7020   $1,280.70   $1,280.75   $1,280.60