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 $233.74   13.422%   $265.1126   $265.11   $265.10   $265.10  
  Purchase #2 $86.67   13.365%   $98.2534   $98.25   $98.25   $98.30  
  Purchase #3 $111.36   5.497%   $117.4815   $117.48   $117.50   $117.50  
  Purchase #4 $99.89   4.344%   $104.2292   $104.23   $104.25   $104.20  
  Purchase #5 $132.92   11.401%   $148.0742   $148.07   $148.05   $148.10  
  Purchase #6 $185.71   8.869%   $202.1806   $202.18   $202.20   $202.20  
  Purchase #7 $67.68   12.210%   $75.9437   $75.94   $75.95   $75.90  
  7 purchase totals = $917.97       $1,011.2752   $1,011.26   $1,011.30   $1,011.30