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 $116.34   10.564%   $128.6302   $128.63   $128.65   $128.60  
  Purchase #2 $169.85   4.421%   $177.3591   $177.36   $177.35   $177.40  
  Purchase #3 $157.49   11.568%   $175.7084   $175.71   $175.70   $175.70  
  Purchase #4 $104.67   13.852%   $119.1689   $119.17   $119.15   $119.20  
  Purchase #5 $58.70   6.410%   $62.4627   $62.46   $62.45   $62.50  
  Purchase #6 $57.74   3.465%   $59.7407   $59.74   $59.75   $59.70  
  Purchase #7 $218.58   6.502%   $232.7921   $232.79   $232.80   $232.80  
  7 purchase totals = $883.37       $955.8621   $955.86   $955.85   $955.90