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 $219.93   13.200%   $248.9608   $248.96   $248.95   $249.00  
  Purchase #2 $94.50   9.572%   $103.5455   $103.55   $103.55   $103.50  
  Purchase #3 $64.84   5.809%   $68.6066   $68.61   $68.60   $68.60  
  Purchase #4 $176.56   9.132%   $192.6835   $192.68   $192.70   $192.70  
  Purchase #5 $60.90   7.368%   $65.3871   $65.39   $65.40   $65.40  
  Purchase #6 $48.75   8.244%   $52.769   $52.77   $52.75   $52.80  
  Purchase #7 $169.69   3.788%   $176.1179   $176.12   $176.10   $176.10  
  7 purchase totals = $835.17       $908.0704   $908.08   $908.05   $908.10