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 $244.66   9.632%   $268.2257   $268.23   $268.25   $268.20  
  Purchase #2 $25.47   3.125%   $26.2659   $26.27   $26.25   $26.30  
  Purchase #3 $184.97   3.652%   $191.7251   $191.73   $191.75   $191.70  
  Purchase #4 $57.94   5.202%   $60.954   $60.95   $60.95   $61.00  
  Purchase #5 $109.90   13.749%   $125.0102   $125.01   $125.00   $125.00  
  Purchase #6 $167.66   10.188%   $184.7412   $184.74   $184.75   $184.70  
  Purchase #7 $59.83   7.469%   $64.2987   $64.30   $64.30   $64.30  
  7 purchase totals = $850.43       $921.2208   $921.23   $921.25   $921.20