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 $101.59   4.860%   $106.5273   $106.53   $106.55   $106.50  
  Purchase #2 $176.60   10.844%   $195.7505   $195.75   $195.75   $195.80  
  Purchase #3 $42.38   8.848%   $46.1298   $46.13   $46.15   $46.10  
  Purchase #4 $47.38   3.780%   $49.171   $49.17   $49.15   $49.20  
  Purchase #5 $37.96   12.254%   $42.6116   $42.61   $42.60   $42.60  
  Purchase #6 $243.37   5.765%   $257.4003   $257.40   $257.40   $257.40  
  Purchase #7 $19.47   7.713%   $20.9717   $20.97   $20.95   $21.00  
  7 purchase totals = $668.75       $718.5622   $718.56   $718.55   $718.60