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 $236.85   12.283%   $265.9423   $265.94   $265.95   $265.90  
  Purchase #2 $60.49   3.536%   $62.6289   $62.63   $62.65   $62.60  
  Purchase #3 $68.91   10.555%   $76.1835   $76.18   $76.20   $76.20  
  Purchase #4 $126.93   10.525%   $140.2894   $140.29   $140.30   $140.30  
  Purchase #5 $36.95   13.569%   $41.9637   $41.96   $41.95   $42.00  
  Purchase #6 $102.58   13.224%   $116.1452   $116.15   $116.15   $116.10  
  Purchase #7 $51.91   5.710%   $54.8741   $54.87   $54.85   $54.90  
  7 purchase totals = $684.62       $758.0271   $758.02   $758.05   $758.00