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 $61.65   3.239%   $63.6468   $63.65   $63.65   $63.60  
  Purchase #2 $115.59   6.530%   $123.138   $123.14   $123.15   $123.10  
  Purchase #3 $40.74   10.525%   $45.0279   $45.03   $45.05   $45.00  
  Purchase #4 $54.86   7.153%   $58.7841   $58.78   $58.80   $58.80  
  Purchase #5 $59.36   12.218%   $66.6126   $66.61   $66.60   $66.60  
  Purchase #6 $125.58   3.858%   $130.4249   $130.42   $130.40   $130.40  
  Purchase #7 $181.71   12.364%   $204.1766   $204.18   $204.20   $204.20  
  7 purchase totals = $639.49       $691.8109   $691.81   $691.85   $691.70