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 $191.68   6.287%   $203.7309   $203.73   $203.75   $203.70  
  Purchase #2 $11.78   7.722%   $12.6897   $12.69   $12.70   $12.70  
  Purchase #3 $206.51   13.602%   $234.5995   $234.60   $234.60   $234.60  
  Purchase #4 $107.61   11.663%   $120.1606   $120.16   $120.15   $120.20  
  Purchase #5 $101.61   4.272%   $105.9508   $105.95   $105.95   $106.00  
  Purchase #6 $74.55   10.263%   $82.2011   $82.20   $82.20   $82.20  
  Purchase #7 $40.63   13.861%   $46.2617   $46.26   $46.25   $46.30  
  7 purchase totals = $734.37       $805.5943   $805.59   $805.60   $805.70