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 $56.37   8.724%   $61.2877   $61.29   $61.30   $61.30  
  Purchase #2 $30.60   7.291%   $32.831   $32.83   $32.85   $32.80  
  Purchase #3 $67.47   6.147%   $71.6174   $71.62   $71.60   $71.60  
  Purchase #4 $13.67   7.776%   $14.733   $14.73   $14.75   $14.70  
  Purchase #5 $248.49   3.627%   $257.5027   $257.50   $257.50   $257.50  
  Purchase #6 $54.79   7.374%   $58.8302   $58.83   $58.85   $58.80  
  Purchase #7 $223.29   9.356%   $244.181   $244.18   $244.20   $244.20  
  7 purchase totals = $694.68       $740.9830   $740.98   $741.05   $740.90