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 $29.92   11.102%   $33.2417   $33.24   $33.25   $33.20  
  Purchase #2 $111.62   12.389%   $125.4486   $125.45   $125.45   $125.40  
  Purchase #3 $233.77   5.493%   $246.611   $246.61   $246.60   $246.60  
  Purchase #4 $204.92   11.381%   $228.2419   $228.24   $228.25   $228.20  
  Purchase #5 $178.56   7.840%   $192.5591   $192.56   $192.55   $192.60  
  Purchase #6 $115.47   13.341%   $130.8749   $130.87   $130.85   $130.90  
  Purchase #7 $52.30   11.649%   $58.3924   $58.39   $58.40   $58.40  
  7 purchase totals = $926.56       $1,015.3696   $1,015.36   $1,015.35   $1,015.30