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 $31.38   11.308%   $34.9285   $34.93   $34.95   $34.90  
  Purchase #2 $96.33   3.157%   $99.3711   $99.37   $99.35   $99.40  
  Purchase #3 $237.84   8.322%   $257.633   $257.63   $257.65   $257.60  
  Purchase #4 $148.27   3.291%   $153.1496   $153.15   $153.15   $153.10  
  Purchase #5 $212.89   4.104%   $221.627   $221.63   $221.65   $221.60  
  Purchase #6 $50.96   7.867%   $54.969   $54.97   $54.95   $55.00  
  Purchase #7 $26.78   5.311%   $28.2023   $28.20   $28.20   $28.20  
  7 purchase totals = $804.45       $849.8805   $849.88   $849.90   $849.80