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 $111.99   12.553%   $126.0481   $126.05   $126.05   $126.00  
  Purchase #2 $117.87   10.136%   $129.8173   $129.82   $129.80   $129.80  
  Purchase #3 $189.34   7.164%   $202.9043   $202.90   $202.90   $202.90  
  Purchase #4 $209.42   10.775%   $231.985   $231.99   $232.00   $232.00  
  Purchase #5 $50.59   8.564%   $54.9225   $54.92   $54.90   $54.90  
  Purchase #6 $211.87   11.452%   $236.1334   $236.13   $236.15   $236.10  
  Purchase #7 $222.99   5.249%   $234.6947   $234.69   $234.70   $234.70  
  7 purchase totals = $1,114.07       $1,216.5053   $1,216.50   $1,216.50   $1,216.40