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 $24.25   5.784%   $25.6526   $25.65   $25.65   $25.70  
  Purchase #2 $76.39   13.773%   $86.9112   $86.91   $86.90   $86.90  
  Purchase #3 $203.53   3.468%   $210.5884   $210.59   $210.60   $210.60  
  Purchase #4 $248.74   6.694%   $265.3907   $265.39   $265.40   $265.40  
  Purchase #5 $153.69   9.594%   $168.435   $168.44   $168.45   $168.40  
  Purchase #6 $54.67   12.285%   $61.3862   $61.39   $61.40   $61.40  
  Purchase #7 $140.75   5.116%   $147.9508   $147.95   $147.95   $148.00  
  7 purchase totals = $902.02       $966.3149   $966.32   $966.35   $966.40