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 $76.75   9.122%   $83.7511   $83.75   $83.75   $83.80  
  Purchase #2 $237.57   11.840%   $265.6983   $265.70   $265.70   $265.70  
  Purchase #3 $156.36   4.825%   $163.9044   $163.90   $163.90   $163.90  
  Purchase #4 $217.38   10.735%   $240.7157   $240.72   $240.70   $240.70  
  Purchase #5 $218.80   8.457%   $237.3039   $237.30   $237.30   $237.30  
  Purchase #6 $158.32   13.314%   $179.3987   $179.40   $179.40   $179.40  
  Purchase #7 $170.45   3.339%   $176.1413   $176.14   $176.15   $176.10  
  7 purchase totals = $1,235.63       $1,346.9134   $1,346.91   $1,346.90   $1,346.90