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 $61.67   3.182%   $63.6323   $63.63   $63.65   $63.60  
  Purchase #2 $48.37   5.385%   $50.9747   $50.97   $50.95   $51.00  
  Purchase #3 $202.89   6.116%   $215.2988   $215.30   $215.30   $215.30  
  Purchase #4 $98.94   5.129%   $104.0146   $104.01   $104.00   $104.00  
  Purchase #5 $154.83   7.751%   $166.8309   $166.83   $166.85   $166.80  
  Purchase #6 $95.60   9.248%   $104.4411   $104.44   $104.45   $104.40  
  Purchase #7 $30.60   13.130%   $34.6178   $34.62   $34.60   $34.60  
  7 purchase totals = $692.90       $739.8102   $739.80   $739.80   $739.70