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 $202.73   8.763%   $220.4952   $220.50   $220.50   $220.50  
  Purchase #2 $247.49   11.494%   $275.9365   $275.94   $275.95   $275.90  
  Purchase #3 $161.53   13.597%   $183.4932   $183.49   $183.50   $183.50  
  Purchase #4 $57.99   6.186%   $61.5773   $61.58   $61.60   $61.60  
  Purchase #5 $247.92   5.543%   $261.6622   $261.66   $261.65   $261.70  
  Purchase #6 $85.65   12.369%   $96.244   $96.24   $96.25   $96.20  
  Purchase #7 $106.81   4.683%   $111.8119   $111.81   $111.80   $111.80  
  7 purchase totals = $1,110.12       $1,211.2203   $1,211.22   $1,211.25   $1,211.20