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 $206.92   9.552%   $226.685   $226.69   $226.70   $226.70  
  Purchase #2 $70.45   9.279%   $76.9871   $76.99   $77.00   $77.00  
  Purchase #3 $61.62   4.293%   $64.2653   $64.27   $64.25   $64.30  
  Purchase #4 $64.55   5.704%   $68.2319   $68.23   $68.25   $68.20  
  Purchase #5 $151.45   12.295%   $170.0708   $170.07   $170.05   $170.10  
  Purchase #6 $246.48   5.249%   $259.4177   $259.42   $259.40   $259.40  
  Purchase #7 $94.26   10.557%   $104.211   $104.21   $104.20   $104.20  
  7 purchase totals = $895.73       $969.8688   $969.88   $969.85   $969.90