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 $244.41   11.699%   $273.0035   $273.00   $273.00   $273.00  
  Purchase #2 $74.66   11.165%   $82.9958   $83.00   $83.00   $83.00  
  Purchase #3 $187.53   13.670%   $213.1654   $213.17   $213.15   $213.20  
  Purchase #4 $163.33   3.658%   $169.3046   $169.30   $169.30   $169.30  
  Purchase #5 $68.70   11.537%   $76.6259   $76.63   $76.65   $76.60  
  Purchase #6 $73.51   11.438%   $81.9181   $81.92   $81.90   $81.90  
  Purchase #7 $151.78   12.811%   $171.2245   $171.22   $171.20   $171.20  
  7 purchase totals = $963.92       $1,068.2378   $1,068.24   $1,068.20   $1,068.20