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 $110.38   8.167%   $119.3947   $119.39   $119.40   $119.40  
  Purchase #2 $243.26   11.612%   $271.5074   $271.51   $271.50   $271.50  
  Purchase #3 $98.60   6.252%   $104.7645   $104.76   $104.75   $104.80  
  Purchase #4 $117.82   7.521%   $126.6812   $126.68   $126.70   $126.70  
  Purchase #5 $81.44   6.820%   $86.9942   $86.99   $87.00   $87.00  
  Purchase #6 $67.99   6.458%   $72.3808   $72.38   $72.40   $72.40  
  Purchase #7 $227.74   4.165%   $237.2254   $237.23   $237.25   $237.20  
  7 purchase totals = $947.23       $1,018.9482   $1,018.94   $1,019.00   $1,019.00