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 $194.39   9.434%   $212.7288   $212.73   $212.75   $212.70  
  Purchase #2 $111.87   11.409%   $124.6332   $124.63   $124.65   $124.60  
  Purchase #3 $62.48   4.553%   $65.3247   $65.32   $65.30   $65.30  
  Purchase #4 $22.99   11.229%   $25.5715   $25.57   $25.55   $25.60  
  Purchase #5 $199.87   7.381%   $214.6224   $214.62   $214.60   $214.60  
  Purchase #6 $29.95   3.111%   $30.8817   $30.88   $30.90   $30.90  
  Purchase #7 $39.36   9.268%   $43.0079   $43.01   $43.00   $43.00  
  7 purchase totals = $660.91       $716.7702   $716.76   $716.75   $716.70