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 $235.82   3.269%   $243.529   $243.53   $243.55   $243.50  
  Purchase #2 $14.26   9.628%   $15.633   $15.63   $15.65   $15.60  
  Purchase #3 $161.62   5.825%   $171.0344   $171.03   $171.05   $171.00  
  Purchase #4 $89.64   5.476%   $94.5487   $94.55   $94.55   $94.50  
  Purchase #5 $94.42   8.798%   $102.7271   $102.73   $102.75   $102.70  
  Purchase #6 $105.30   13.274%   $119.2775   $119.28   $119.30   $119.30  
  Purchase #7 $82.90   5.228%   $87.234   $87.23   $87.25   $87.20  
  7 purchase totals = $783.96       $833.9837   $833.98   $834.10   $833.80