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 $201.50   8.206%   $218.0351   $218.04   $218.05   $218.00  
  Purchase #2 $205.93   8.207%   $222.8307   $222.83   $222.85   $222.80  
  Purchase #3 $95.37   9.192%   $104.1364   $104.14   $104.15   $104.10  
  Purchase #4 $82.26   8.378%   $89.1517   $89.15   $89.15   $89.20  
  Purchase #5 $166.28   3.617%   $172.2943   $172.29   $172.30   $172.30  
  Purchase #6 $245.30   6.521%   $261.296   $261.30   $261.30   $261.30  
  Purchase #7 $150.63   12.278%   $169.1244   $169.12   $169.10   $169.10  
  7 purchase totals = $1,147.27       $1,236.8686   $1,236.87   $1,236.90   $1,236.80