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 $222.75   8.776%   $242.2985   $242.30   $242.30   $242.30  
  Purchase #2 $228.92   7.508%   $246.1073   $246.11   $246.10   $246.10  
  Purchase #3 $166.99   10.561%   $184.6258   $184.63   $184.65   $184.60  
  Purchase #4 $133.81   12.449%   $150.468   $150.47   $150.45   $150.50  
  Purchase #5 $236.71   9.627%   $259.4981   $259.50   $259.50   $259.50  
  Purchase #6 $56.74   5.649%   $59.9452   $59.95   $59.95   $59.90  
  Purchase #7 $164.30   11.265%   $182.8084   $182.81   $182.80   $182.80  
  7 purchase totals = $1,210.22       $1,325.7513   $1,325.77   $1,325.75   $1,325.70