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 $112.66   12.762%   $127.0377   $127.04   $127.05   $127.00  
  Purchase #2 $179.29   8.266%   $194.1101   $194.11   $194.10   $194.10  
  Purchase #3 $101.48   8.351%   $109.9546   $109.95   $109.95   $110.00  
  Purchase #4 $180.86   6.455%   $192.5345   $192.53   $192.55   $192.50  
  Purchase #5 $124.83   4.493%   $130.4386   $130.44   $130.45   $130.40  
  Purchase #6 $42.44   11.836%   $47.4632   $47.46   $47.45   $47.50  
  Purchase #7 $66.52   11.110%   $73.9104   $73.91   $73.90   $73.90  
  7 purchase totals = $808.08       $875.4491   $875.44   $875.45   $875.40