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 $187.63   6.448%   $199.7284   $199.73   $199.75   $199.70  
  Purchase #2 $154.50   13.210%   $174.9095   $174.91   $174.90   $174.90  
  Purchase #3 $137.30   9.446%   $150.2694   $150.27   $150.25   $150.30  
  Purchase #4 $23.35   4.850%   $24.4825   $24.48   $24.50   $24.50  
  Purchase #5 $101.78   4.480%   $106.3397   $106.34   $106.35   $106.30  
  Purchase #6 $183.93   3.338%   $190.0696   $190.07   $190.05   $190.10  
  Purchase #7 $248.80   5.776%   $263.1707   $263.17   $263.15   $263.20  
  7 purchase totals = $1,037.29       $1,108.9698   $1,108.97   $1,108.95   $1,109.00