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 $226.60   6.594%   $241.542   $241.54   $241.55   $241.50  
  Purchase #2 $41.87   5.783%   $44.2913   $44.29   $44.30   $44.30  
  Purchase #3 $93.41   11.725%   $104.3623   $104.36   $104.35   $104.40  
  Purchase #4 $36.31   8.429%   $39.3706   $39.37   $39.35   $39.40  
  Purchase #5 $171.91   7.787%   $185.2966   $185.30   $185.30   $185.30  
  Purchase #6 $59.54   9.176%   $65.0034   $65.00   $65.00   $65.00  
  Purchase #7 $233.73   4.412%   $244.0422   $244.04   $244.05   $244.00  
  7 purchase totals = $863.37       $923.9084   $923.90   $923.90   $923.90