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 $29.55   10.198%   $32.5635   $32.56   $32.55   $32.60  
  Purchase #2 $25.66   3.757%   $26.624   $26.62   $26.60   $26.60  
  Purchase #3 $171.96   13.628%   $195.3947   $195.39   $195.40   $195.40  
  Purchase #4 $151.76   11.329%   $168.9529   $168.95   $168.95   $169.00  
  Purchase #5 $16.83   7.425%   $18.0796   $18.08   $18.10   $18.10  
  Purchase #6 $83.85   3.521%   $86.8024   $86.80   $86.80   $86.80  
  Purchase #7 $195.62   5.415%   $206.2128   $206.21   $206.20   $206.20  
  7 purchase totals = $675.23       $734.6299   $734.61   $734.60   $734.70