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 $246.51   11.387%   $274.5801   $274.58   $274.60   $274.60  
  Purchase #2 $33.42   5.193%   $35.1555   $35.16   $35.15   $35.20  
  Purchase #3 $250.37   13.113%   $283.201   $283.20   $283.20   $283.20  
  Purchase #4 $238.79   13.449%   $270.9049   $270.90   $270.90   $270.90  
  Purchase #5 $116.77   7.852%   $125.9388   $125.94   $125.95   $125.90  
  Purchase #6 $174.56   6.158%   $185.3094   $185.31   $185.30   $185.30  
  Purchase #7 $103.73   7.397%   $111.4029   $111.40   $111.40   $111.40  
  7 purchase totals = $1,164.15       $1,286.4926   $1,286.49   $1,286.50   $1,286.50