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 $239.98   3.695%   $248.8473   $248.85   $248.85   $248.80  
  Purchase #2 $159.69   5.821%   $168.9856   $168.99   $169.00   $169.00  
  Purchase #3 $74.36   10.823%   $82.408   $82.41   $82.40   $82.40  
  Purchase #4 $217.28   3.399%   $224.6653   $224.67   $224.65   $224.70  
  Purchase #5 $168.26   3.474%   $174.1054   $174.11   $174.10   $174.10  
  Purchase #6 $218.84   6.491%   $233.0449   $233.04   $233.05   $233.00  
  Purchase #7 $68.39   5.222%   $71.9613   $71.96   $71.95   $72.00  
  7 purchase totals = $1,146.80       $1,204.0178   $1,204.03   $1,204.00   $1,204.00