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 $217.86   11.204%   $242.269   $242.27   $242.25   $242.30  
  Purchase #2 $90.27   13.776%   $102.7056   $102.71   $102.70   $102.70  
  Purchase #3 $136.91   12.184%   $153.5911   $153.59   $153.60   $153.60  
  Purchase #4 $44.69   3.319%   $46.1733   $46.17   $46.15   $46.20  
  Purchase #5 $42.40   6.638%   $45.2145   $45.21   $45.20   $45.20  
  Purchase #6 $248.65   3.659%   $257.7481   $257.75   $257.75   $257.70  
  Purchase #7 $184.43   5.443%   $194.4685   $194.47   $194.45   $194.50  
  7 purchase totals = $965.21       $1,042.1701   $1,042.17   $1,042.10   $1,042.20