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 $217.47   13.397%   $246.6045   $246.60   $246.60   $246.60  
  Purchase #2 $226.63   7.674%   $244.0216   $244.02   $244.00   $244.00  
  Purchase #3 $36.38   5.280%   $38.3009   $38.30   $38.30   $38.30  
  Purchase #4 $213.86   13.398%   $242.513   $242.51   $242.50   $242.50  
  Purchase #5 $95.87   10.176%   $105.6257   $105.63   $105.65   $105.60  
  Purchase #6 $174.29   8.744%   $189.5299   $189.53   $189.55   $189.50  
  Purchase #7 $32.31   12.567%   $36.3704   $36.37   $36.35   $36.40  
  7 purchase totals = $996.81       $1,102.9660   $1,102.96   $1,102.95   $1,102.90