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 $217.54   6.477%   $231.6301   $231.63   $231.65   $231.60  
  Purchase #2 $41.98   10.744%   $46.4903   $46.49   $46.50   $46.50  
  Purchase #3 $97.64   9.366%   $106.785   $106.79   $106.80   $106.80  
  Purchase #4 $61.82   11.282%   $68.7945   $68.79   $68.80   $68.80  
  Purchase #5 $113.55   3.448%   $117.4652   $117.47   $117.45   $117.50  
  Purchase #6 $158.58   10.771%   $175.6607   $175.66   $175.65   $175.70  
  Purchase #7 $70.35   8.300%   $76.1891   $76.19   $76.20   $76.20  
  7 purchase totals = $761.46       $823.0149   $823.02   $823.05   $823.10