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 $244.98   3.761%   $254.1937   $254.19   $254.20   $254.20  
  Purchase #2 $170.41   9.443%   $186.5018   $186.50   $186.50   $186.50  
  Purchase #3 $229.26   11.742%   $256.1797   $256.18   $256.20   $256.20  
  Purchase #4 $101.43   8.735%   $110.2899   $110.29   $110.30   $110.30  
  Purchase #5 $18.65   9.277%   $20.3802   $20.38   $20.40   $20.40  
  Purchase #6 $45.56   12.338%   $51.1812   $51.18   $51.20   $51.20  
  Purchase #7 $160.29   3.508%   $165.913   $165.91   $165.90   $165.90  
  7 purchase totals = $970.58       $1,044.6395   $1,044.63   $1,044.70   $1,044.70