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 $52.68   12.422%   $59.2239   $59.22   $59.20   $59.20  
  Purchase #2 $242.43   3.299%   $250.4278   $250.43   $250.45   $250.40  
  Purchase #3 $215.93   3.535%   $223.5631   $223.56   $223.55   $223.60  
  Purchase #4 $17.38   3.223%   $17.9402   $17.94   $17.95   $17.90  
  Purchase #5 $132.90   11.379%   $148.0227   $148.02   $148.00   $148.00  
  Purchase #6 $14.92   13.854%   $16.987   $16.99   $17.00   $17.00  
  Purchase #7 $31.85   7.570%   $34.261   $34.26   $34.25   $34.30  
  7 purchase totals = $708.09       $750.4257   $750.42   $750.40   $750.40