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 $187.58   9.614%   $205.6139   $205.61   $205.60   $205.60  
  Purchase #2 $237.69   11.628%   $265.3286   $265.33   $265.35   $265.30  
  Purchase #3 $182.33   4.637%   $190.7846   $190.78   $190.80   $190.80  
  Purchase #4 $224.79   13.356%   $254.813   $254.81   $254.80   $254.80  
  Purchase #5 $244.30   4.488%   $255.2642   $255.26   $255.25   $255.30  
  Purchase #6 $126.78   5.595%   $133.8733   $133.87   $133.85   $133.90  
  Purchase #7 $88.47   9.712%   $97.0622   $97.06   $97.05   $97.10  
  7 purchase totals = $1,291.94       $1,402.7398   $1,402.72   $1,402.70   $1,402.80