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 $57.27   6.664%   $61.0865   $61.09   $61.10   $61.10  
  Purchase #2 $227.92   3.495%   $235.8858   $235.89   $235.90   $235.90  
  Purchase #3 $46.58   3.142%   $48.0435   $48.04   $48.05   $48.00  
  Purchase #4 $249.73   11.308%   $277.9695   $277.97   $277.95   $278.00  
  Purchase #5 $152.42   7.429%   $163.7433   $163.74   $163.75   $163.70  
  Purchase #6 $42.38   13.342%   $48.0343   $48.03   $48.05   $48.00  
  Purchase #7 $157.41   11.666%   $175.7735   $175.77   $175.75   $175.80  
  7 purchase totals = $933.71       $1,010.5364   $1,010.53   $1,010.55   $1,010.50