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 $244.88   5.751%   $258.963   $258.96   $258.95   $259.00  
  Purchase #2 $195.99   11.191%   $217.9232   $217.92   $217.90   $217.90  
  Purchase #3 $170.95   8.712%   $185.8432   $185.84   $185.85   $185.80  
  Purchase #4 $53.39   7.319%   $57.2976   $57.30   $57.30   $57.30  
  Purchase #5 $109.85   5.697%   $116.1082   $116.11   $116.10   $116.10  
  Purchase #6 $113.74   10.689%   $125.8977   $125.90   $125.90   $125.90  
  Purchase #7 $165.53   10.547%   $182.9884   $182.99   $183.00   $183.00  
  7 purchase totals = $1,054.33       $1,145.0213   $1,145.02   $1,145.00   $1,145.00