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 $226.89   12.565%   $255.3987   $255.40   $255.40   $255.40  
  Purchase #2 $90.29   6.302%   $95.9801   $95.98   $96.00   $96.00  
  Purchase #3 $78.96   7.456%   $84.8473   $84.85   $84.85   $84.80  
  Purchase #4 $22.54   6.826%   $24.0786   $24.08   $24.10   $24.10  
  Purchase #5 $196.26   13.366%   $222.4921   $222.49   $222.50   $222.50  
  Purchase #6 $60.63   5.743%   $64.112   $64.11   $64.10   $64.10  
  Purchase #7 $215.84   9.465%   $236.2693   $236.27   $236.25   $236.30  
  7 purchase totals = $891.41       $983.1781   $983.18   $983.20   $983.20