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 $59.95   11.494%   $66.8407   $66.84   $66.85   $66.80  
  Purchase #2 $237.78   4.541%   $248.5776   $248.58   $248.60   $248.60  
  Purchase #3 $103.99   9.578%   $113.9502   $113.95   $113.95   $114.00  
  Purchase #4 $69.89   10.475%   $77.211   $77.21   $77.20   $77.20  
  Purchase #5 $159.34   10.613%   $176.2508   $176.25   $176.25   $176.30  
  Purchase #6 $52.90   9.505%   $57.9281   $57.93   $57.95   $57.90  
  Purchase #7 $248.41   6.173%   $263.7443   $263.74   $263.75   $263.70  
  7 purchase totals = $932.26       $1,004.5027   $1,004.50   $1,004.55   $1,004.50