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 $242.51   11.166%   $269.5887   $269.59   $269.60   $269.60  
  Purchase #2 $99.44   13.261%   $112.6267   $112.63   $112.65   $112.60  
  Purchase #3 $238.40   11.739%   $266.3858   $266.39   $266.40   $266.40  
  Purchase #4 $195.55   8.571%   $212.3106   $212.31   $212.30   $212.30  
  Purchase #5 $110.46   7.674%   $118.9367   $118.94   $118.95   $118.90  
  Purchase #6 $5.25   4.217%   $5.4714   $5.47   $5.45   $5.50  
  Purchase #7 $236.27   5.129%   $248.3883   $248.39   $248.40   $248.40  
  7 purchase totals = $1,127.88       $1,233.7082   $1,233.72   $1,233.75   $1,233.70