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 $117.65   6.574%   $125.3843   $125.38   $125.40   $125.40  
  Purchase #2 $41.91   9.203%   $45.767   $45.77   $45.75   $45.80  
  Purchase #3 $22.47   6.798%   $23.9975   $24.00   $24.00   $24.00  
  Purchase #4 $244.41   12.344%   $274.58   $274.58   $274.60   $274.60  
  Purchase #5 $220.34   10.872%   $244.2954   $244.30   $244.30   $244.30  
  Purchase #6 $116.81   13.271%   $132.3119   $132.31   $132.30   $132.30  
  Purchase #7 $200.65   10.766%   $222.252   $222.25   $222.25   $222.30  
  7 purchase totals = $964.24       $1,068.5881   $1,068.59   $1,068.60   $1,068.70