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 $32.62   8.732%   $35.4684   $35.47   $35.45   $35.50  
  Purchase #2 $153.45   6.452%   $163.3506   $163.35   $163.35   $163.40  
  Purchase #3 $24.90   6.662%   $26.5588   $26.56   $26.55   $26.60  
  Purchase #4 $154.38   4.334%   $161.0708   $161.07   $161.05   $161.10  
  Purchase #5 $212.75   4.143%   $221.5642   $221.56   $221.55   $221.60  
  Purchase #6 $245.61   13.776%   $279.4452   $279.45   $279.45   $279.40  
  Purchase #7 $27.37   6.831%   $29.2396   $29.24   $29.25   $29.20  
  7 purchase totals = $851.08       $916.6976   $916.70   $916.65   $916.80