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 $64.83   3.121%   $66.8533   $66.85   $66.85   $66.90  
  Purchase #2 $24.31   6.111%   $25.7956   $25.80   $25.80   $25.80  
  Purchase #3 $15.48   10.181%   $17.056   $17.06   $17.05   $17.10  
  Purchase #4 $183.57   6.643%   $195.7646   $195.76   $195.75   $195.80  
  Purchase #5 $109.97   6.450%   $117.0631   $117.06   $117.05   $117.10  
  Purchase #6 $216.67   4.719%   $226.8947   $226.89   $226.90   $226.90  
  Purchase #7 $79.60   9.187%   $86.9129   $86.91   $86.90   $86.90  
  7 purchase totals = $694.43       $736.3402   $736.33   $736.30   $736.50