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 $79.59   12.578%   $89.6008   $89.60   $89.60   $89.60  
  Purchase #2 $54.39   13.381%   $61.6679   $61.67   $61.65   $61.70  
  Purchase #3 $60.68   4.398%   $63.3487   $63.35   $63.35   $63.30  
  Purchase #4 $73.99   3.147%   $76.3185   $76.32   $76.30   $76.30  
  Purchase #5 $182.58   7.872%   $196.9527   $196.95   $196.95   $197.00  
  Purchase #6 $124.84   11.625%   $139.3527   $139.35   $139.35   $139.40  
  Purchase #7 $119.33   13.187%   $135.066   $135.07   $135.05   $135.10  
  7 purchase totals = $695.40       $762.3073   $762.31   $762.25   $762.40