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 $58.74   8.663%   $63.8286   $63.83   $63.85   $63.80  
  Purchase #2 $184.46   11.818%   $206.2595   $206.26   $206.25   $206.30  
  Purchase #3 $11.84   3.682%   $12.2759   $12.28   $12.30   $12.30  
  Purchase #4 $207.57   13.829%   $236.2749   $236.27   $236.25   $236.30  
  Purchase #5 $103.50   11.708%   $115.6178   $115.62   $115.60   $115.60  
  Purchase #6 $95.98   8.489%   $104.1277   $104.13   $104.15   $104.10  
  Purchase #7 $67.54   13.397%   $76.5883   $76.59   $76.60   $76.60  
  7 purchase totals = $729.63       $814.9727   $814.98   $815.00   $815.00