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 $215.44   13.203%   $243.8845   $243.88   $243.90   $243.90  
  Purchase #2 $211.51   10.183%   $233.0481   $233.05   $233.05   $233.00  
  Purchase #3 $181.59   12.682%   $204.6192   $204.62   $204.60   $204.60  
  Purchase #4 $90.98   5.602%   $96.0767   $96.08   $96.10   $96.10  
  Purchase #5 $250.56   4.504%   $261.8452   $261.85   $261.85   $261.80  
  Purchase #6 $214.47   11.175%   $238.437   $238.44   $238.45   $238.40  
  Purchase #7 $68.69   7.832%   $74.0698   $74.07   $74.05   $74.10  
  7 purchase totals = $1,233.24       $1,351.9805   $1,351.99   $1,352.00   $1,351.90