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 $228.95   3.326%   $236.5649   $236.56   $236.55   $236.60  
  Purchase #2 $110.61   13.305%   $125.3267   $125.33   $125.35   $125.30  
  Purchase #3 $38.83   4.842%   $40.7101   $40.71   $40.70   $40.70  
  Purchase #4 $215.34   11.284%   $239.639   $239.64   $239.65   $239.60  
  Purchase #5 $188.44   11.174%   $209.4963   $209.50   $209.50   $209.50  
  Purchase #6 $211.35   13.339%   $239.542   $239.54   $239.55   $239.50  
  Purchase #7 $224.64   8.304%   $243.2941   $243.29   $243.30   $243.30  
  7 purchase totals = $1,218.16       $1,334.5731   $1,334.57   $1,334.60   $1,334.50