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 $241.83   9.311%   $264.3468   $264.35   $264.35   $264.30  
  Purchase #2 $114.35   3.367%   $118.2002   $118.20   $118.20   $118.20  
  Purchase #3 $168.93   13.184%   $191.2017   $191.20   $191.20   $191.20  
  Purchase #4 $96.44   7.676%   $103.8427   $103.84   $103.85   $103.80  
  Purchase #5 $248.52   12.617%   $279.8758   $279.88   $279.90   $279.90  
  Purchase #6 $229.95   4.255%   $239.7344   $239.73   $239.75   $239.70  
  Purchase #7 $12.87   11.672%   $14.3722   $14.37   $14.35   $14.40  
  7 purchase totals = $1,112.89       $1,211.5738   $1,211.57   $1,211.60   $1,211.50