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 $60.90   3.460%   $63.0071   $63.01   $63.00   $63.00  
  Purchase #2 $176.47   3.723%   $183.04   $183.04   $183.05   $183.00  
  Purchase #3 $74.45   12.186%   $83.5225   $83.52   $83.50   $83.50  
  Purchase #4 $192.50   6.754%   $205.5015   $205.50   $205.50   $205.50  
  Purchase #5 $113.61   9.789%   $124.7313   $124.73   $124.75   $124.70  
  Purchase #6 $109.76   6.766%   $117.1864   $117.19   $117.20   $117.20  
  Purchase #7 $9.36   3.473%   $9.6851   $9.69   $9.70   $9.70  
  7 purchase totals = $737.05       $786.6739   $786.68   $786.70   $786.60