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 $24.93   5.267%   $26.2431   $26.24   $26.25   $26.20  
  Purchase #2 $209.34   12.523%   $235.5556   $235.56   $235.55   $235.60  
  Purchase #3 $39.36   8.631%   $42.7572   $42.76   $42.75   $42.80  
  Purchase #4 $37.59   12.611%   $42.3305   $42.33   $42.35   $42.30  
  Purchase #5 $146.97   11.174%   $163.3924   $163.39   $163.40   $163.40  
  Purchase #6 $232.75   10.158%   $256.3927   $256.39   $256.40   $256.40  
  Purchase #7 $206.94   9.145%   $225.8647   $225.86   $225.85   $225.90  
  7 purchase totals = $897.88       $992.5362   $992.53   $992.55   $992.60