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 $211.69   11.496%   $236.0259   $236.03   $236.05   $236.00  
  Purchase #2 $57.70   8.777%   $62.7643   $62.76   $62.75   $62.80  
  Purchase #3 $6.59   11.849%   $7.3708   $7.37   $7.35   $7.40  
  Purchase #4 $37.80   5.241%   $39.7811   $39.78   $39.80   $39.80  
  Purchase #5 $195.61   5.808%   $206.971   $206.97   $206.95   $207.00  
  Purchase #6 $81.49   3.284%   $84.1661   $84.17   $84.15   $84.20  
  Purchase #7 $127.73   5.340%   $134.5508   $134.55   $134.55   $134.60  
  7 purchase totals = $718.61       $771.6300   $771.63   $771.60   $771.80