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 $64.52   13.765%   $73.4012   $73.40   $73.40   $73.40  
  Purchase #2 $94.38   9.730%   $103.5632   $103.56   $103.55   $103.60  
  Purchase #3 $130.43   9.715%   $143.1013   $143.10   $143.10   $143.10  
  Purchase #4 $47.99   8.846%   $52.2352   $52.24   $52.25   $52.20  
  Purchase #5 $195.39   11.829%   $218.5027   $218.50   $218.50   $218.50  
  Purchase #6 $98.39   7.167%   $105.4416   $105.44   $105.45   $105.40  
  Purchase #7 $22.70   4.116%   $23.6343   $23.63   $23.65   $23.60  
  7 purchase totals = $653.80       $719.8795   $719.87   $719.90   $719.80