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 $211.67   13.273%   $239.765   $239.77   $239.75   $239.80  
  Purchase #2 $21.94   11.411%   $24.4436   $24.44   $24.45   $24.40  
  Purchase #3 $237.62   7.137%   $254.5789   $254.58   $254.60   $254.60  
  Purchase #4 $84.53   4.640%   $88.4522   $88.45   $88.45   $88.50  
  Purchase #5 $131.54   5.812%   $139.1851   $139.19   $139.20   $139.20  
  Purchase #6 $216.35   6.284%   $229.9454   $229.95   $229.95   $229.90  
  Purchase #7 $114.54   4.179%   $119.3266   $119.33   $119.35   $119.30  
  7 purchase totals = $1,018.19       $1,095.6968   $1,095.71   $1,095.75   $1,095.70