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 $57.27   11.772%   $64.0118   $64.01   $64.00   $64.00  
  Purchase #2 $157.45   8.609%   $171.0049   $171.00   $171.00   $171.00  
  Purchase #3 $72.25   12.519%   $81.295   $81.30   $81.30   $81.30  
  Purchase #4 $79.52   7.234%   $85.2725   $85.27   $85.25   $85.30  
  Purchase #5 $103.30   8.434%   $112.0123   $112.01   $112.00   $112.00  
  Purchase #6 $231.47   5.732%   $244.7379   $244.74   $244.75   $244.70  
  Purchase #7 $174.69   7.649%   $188.052   $188.05   $188.05   $188.10  
  7 purchase totals = $875.95       $946.3864   $946.38   $946.35   $946.40