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 $218.54   8.141%   $236.3313   $236.33   $236.35   $236.30  
  Purchase #2 $96.67   11.546%   $107.8315   $107.83   $107.85   $107.80  
  Purchase #3 $59.74   3.725%   $61.9653   $61.97   $61.95   $62.00  
  Purchase #4 $242.39   11.121%   $269.3462   $269.35   $269.35   $269.30  
  Purchase #5 $22.69   11.226%   $25.2372   $25.24   $25.25   $25.20  
  Purchase #6 $137.90   9.832%   $151.4583   $151.46   $151.45   $151.50  
  Purchase #7 $168.66   4.219%   $175.7758   $175.78   $175.80   $175.80  
  7 purchase totals = $946.59       $1,027.9456   $1,027.96   $1,028.00   $1,027.90