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 $200.79   12.860%   $226.6116   $226.61   $226.60   $226.60  
  Purchase #2 $125.98   10.753%   $139.5266   $139.53   $139.55   $139.50  
  Purchase #3 $115.44   5.635%   $121.945   $121.95   $121.95   $121.90  
  Purchase #4 $82.48   3.637%   $85.4798   $85.48   $85.50   $85.50  
  Purchase #5 $89.34   9.687%   $97.9944   $97.99   $98.00   $98.00  
  Purchase #6 $99.81   10.508%   $110.298   $110.30   $110.30   $110.30  
  Purchase #7 $77.94   10.157%   $85.8564   $85.86   $85.85   $85.90  
  7 purchase totals = $791.78       $867.7118   $867.72   $867.75   $867.70