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 $118.85   4.537%   $124.2422   $124.24   $124.25   $124.20  
  Purchase #2 $22.85   10.404%   $25.2273   $25.23   $25.25   $25.20  
  Purchase #3 $57.86   7.687%   $62.3077   $62.31   $62.30   $62.30  
  Purchase #4 $159.32   12.764%   $179.6556   $179.66   $179.65   $179.70  
  Purchase #5 $215.34   10.359%   $237.6471   $237.65   $237.65   $237.60  
  Purchase #6 $126.55   8.222%   $136.9549   $136.95   $136.95   $137.00  
  Purchase #7 $165.55   10.513%   $182.9543   $182.95   $182.95   $183.00  
  7 purchase totals = $866.32       $948.9891   $948.99   $949.00   $949.00