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 $191.98   13.394%   $217.6938   $217.69   $217.70   $217.70  
  Purchase #2 $154.25   9.207%   $168.4518   $168.45   $168.45   $168.50  
  Purchase #3 $68.27   5.856%   $72.2679   $72.27   $72.25   $72.30  
  Purchase #4 $10.75   5.560%   $11.3477   $11.35   $11.35   $11.30  
  Purchase #5 $229.62   7.380%   $246.566   $246.57   $246.55   $246.60  
  Purchase #6 $23.84   12.181%   $26.744   $26.74   $26.75   $26.70  
  Purchase #7 $197.38   10.608%   $218.3181   $218.32   $218.30   $218.30  
  7 purchase totals = $876.09       $961.3893   $961.39   $961.35   $961.40