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 $107.60   5.114%   $113.1027   $113.10   $113.10   $113.10  
  Purchase #2 $226.79   12.452%   $255.0299   $255.03   $255.05   $255.00  
  Purchase #3 $64.51   11.325%   $71.8158   $71.82   $71.80   $71.80  
  Purchase #4 $201.33   8.184%   $217.8068   $217.81   $217.80   $217.80  
  Purchase #5 $215.73   4.711%   $225.893   $225.89   $225.90   $225.90  
  Purchase #6 $216.25   9.466%   $236.7202   $236.72   $236.70   $236.70  
  Purchase #7 $82.36   13.535%   $93.5074   $93.51   $93.50   $93.50  
  7 purchase totals = $1,114.57       $1,213.8758   $1,213.88   $1,213.85   $1,213.80