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 $214.51   11.812%   $239.8479   $239.85   $239.85   $239.80  
  Purchase #2 $205.31   6.279%   $218.2014   $218.20   $218.20   $218.20  
  Purchase #3 $250.64   4.594%   $262.1544   $262.15   $262.15   $262.20  
  Purchase #4 $160.78   7.592%   $172.9864   $172.99   $173.00   $173.00  
  Purchase #5 $207.79   10.335%   $229.2651   $229.27   $229.25   $229.30  
  Purchase #6 $32.42   3.576%   $33.5793   $33.58   $33.60   $33.60  
  Purchase #7 $192.76   12.784%   $217.4024   $217.40   $217.40   $217.40  
  7 purchase totals = $1,264.21       $1,373.4369   $1,373.44   $1,373.45   $1,373.50