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 $28.40   8.642%   $30.8543   $30.85   $30.85   $30.90  
  Purchase #2 $220.50   10.304%   $243.2203   $243.22   $243.20   $243.20  
  Purchase #3 $68.73   10.494%   $75.9425   $75.94   $75.95   $75.90  
  Purchase #4 $58.42   5.135%   $61.4199   $61.42   $61.40   $61.40  
  Purchase #5 $5.89   6.267%   $6.2591   $6.26   $6.25   $6.30  
  Purchase #6 $139.47   7.836%   $150.3989   $150.40   $150.40   $150.40  
  Purchase #7 $222.90   6.565%   $237.5334   $237.53   $237.55   $237.50  
  7 purchase totals = $744.31       $805.6284   $805.62   $805.60   $805.60