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 $206.85   13.186%   $234.1252   $234.13   $234.15   $234.10  
  Purchase #2 $244.67   12.517%   $275.2953   $275.30   $275.30   $275.30  
  Purchase #3 $190.47   4.498%   $199.0373   $199.04   $199.05   $199.00  
  Purchase #4 $191.69   5.483%   $202.2004   $202.20   $202.20   $202.20  
  Purchase #5 $94.75   9.460%   $103.7134   $103.71   $103.70   $103.70  
  Purchase #6 $191.81   11.828%   $214.4973   $214.50   $214.50   $214.50  
  Purchase #7 $169.42   3.454%   $175.2718   $175.27   $175.25   $175.30  
  7 purchase totals = $1,289.66       $1,404.1407   $1,404.15   $1,404.15   $1,404.10