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 $221.81   9.234%   $242.2919   $242.29   $242.30   $242.30  
  Purchase #2 $128.39   3.527%   $132.9183   $132.92   $132.90   $132.90  
  Purchase #3 $233.92   3.327%   $241.7025   $241.70   $241.70   $241.70  
  Purchase #4 $22.78   7.273%   $24.4368   $24.44   $24.45   $24.40  
  Purchase #5 $24.68   7.868%   $26.6218   $26.62   $26.60   $26.60  
  Purchase #6 $44.59   9.867%   $48.9897   $48.99   $49.00   $49.00  
  Purchase #7 $230.75   6.224%   $245.1119   $245.11   $245.10   $245.10  
  7 purchase totals = $906.92       $962.0729   $962.07   $962.05   $962.00