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 $244.82   5.802%   $259.0245   $259.02   $259.00   $259.00  
  Purchase #2 $114.31   4.110%   $119.0081   $119.01   $119.00   $119.00  
  Purchase #3 $42.30   3.561%   $43.8063   $43.81   $43.80   $43.80  
  Purchase #4 $82.98   4.439%   $86.6635   $86.66   $86.65   $86.70  
  Purchase #5 $244.40   10.872%   $270.9712   $270.97   $270.95   $271.00  
  Purchase #6 $230.27   9.296%   $251.6759   $251.68   $251.70   $251.70  
  Purchase #7 $125.42   3.520%   $129.8348   $129.83   $129.85   $129.80  
  7 purchase totals = $1,084.50       $1,160.9843   $1,160.98   $1,160.95   $1,161.00