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 $179.36   8.141%   $193.9617   $193.96   $193.95   $194.00  
  Purchase #2 $117.93   8.180%   $127.5767   $127.58   $127.60   $127.60  
  Purchase #3 $110.48   6.737%   $117.923   $117.92   $117.90   $117.90  
  Purchase #4 $43.38   3.674%   $44.9738   $44.97   $44.95   $45.00  
  Purchase #5 $247.76   5.778%   $262.0756   $262.08   $262.10   $262.10  
  Purchase #6 $46.94   6.447%   $49.9662   $49.97   $49.95   $50.00  
  Purchase #7 $91.28   9.705%   $100.1387   $100.14   $100.15   $100.10  
  7 purchase totals = $837.13       $896.6157   $896.62   $896.60   $896.70