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 $244.69   7.229%   $262.3786   $262.38   $262.40   $262.40  
  Purchase #2 $205.91   4.330%   $214.8259   $214.83   $214.85   $214.80  
  Purchase #3 $94.25   3.734%   $97.7693   $97.77   $97.75   $97.80  
  Purchase #4 $44.57   11.671%   $49.7718   $49.77   $49.75   $49.80  
  Purchase #5 $52.43   11.444%   $58.4301   $58.43   $58.45   $58.40  
  Purchase #6 $195.63   13.395%   $221.8346   $221.83   $221.85   $221.80  
  Purchase #7 $123.82   11.507%   $138.068   $138.07   $138.05   $138.10  
  7 purchase totals = $961.30       $1,043.0783   $1,043.08   $1,043.10   $1,043.10