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 $105.48   4.761%   $110.5019   $110.50   $110.50   $110.50  
  Purchase #2 $183.96   11.853%   $205.7648   $205.76   $205.75   $205.80  
  Purchase #3 $50.63   12.812%   $57.1167   $57.12   $57.10   $57.10  
  Purchase #4 $122.78   10.195%   $135.2974   $135.30   $135.30   $135.30  
  Purchase #5 $78.74   13.532%   $89.3951   $89.40   $89.40   $89.40  
  Purchase #6 $13.36   10.376%   $14.7462   $14.75   $14.75   $14.70  
  Purchase #7 $226.50   12.469%   $254.7423   $254.74   $254.75   $254.70  
  7 purchase totals = $781.45       $867.5644   $867.57   $867.55   $867.50