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 $136.48   3.863%   $141.7522   $141.75   $141.75   $141.80  
  Purchase #2 $106.35   9.575%   $116.533   $116.53   $116.55   $116.50  
  Purchase #3 $73.47   4.517%   $76.7886   $76.79   $76.80   $76.80  
  Purchase #4 $87.99   8.201%   $95.2061   $95.21   $95.20   $95.20  
  Purchase #5 $107.32   6.156%   $113.9266   $113.93   $113.95   $113.90  
  Purchase #6 $60.63   12.314%   $68.096   $68.10   $68.10   $68.10  
  Purchase #7 $85.64   3.579%   $88.7051   $88.71   $88.70   $88.70  
  7 purchase totals = $657.88       $701.0076   $701.02   $701.05   $701.00