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 $214.73   7.693%   $231.2492   $231.25   $231.25   $231.20  
  Purchase #2 $119.67   13.355%   $135.6519   $135.65   $135.65   $135.70  
  Purchase #3 $219.42   12.552%   $246.9616   $246.96   $246.95   $247.00  
  Purchase #4 $115.44   5.132%   $121.3644   $121.36   $121.35   $121.40  
  Purchase #5 $125.87   9.604%   $137.9586   $137.96   $137.95   $138.00  
  Purchase #6 $78.49   9.727%   $86.1247   $86.12   $86.10   $86.10  
  Purchase #7 $122.45   3.404%   $126.6182   $126.62   $126.60   $126.60  
  7 purchase totals = $996.07       $1,085.9286   $1,085.92   $1,085.85   $1,086.00