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 $183.63   8.464%   $199.1724   $199.17   $199.15   $199.20  
  Purchase #2 $157.35   7.129%   $168.5675   $168.57   $168.55   $168.60  
  Purchase #3 $134.35   9.692%   $147.3712   $147.37   $147.35   $147.40  
  Purchase #4 $44.97   6.628%   $47.9506   $47.95   $47.95   $48.00  
  Purchase #5 $210.69   3.727%   $218.5424   $218.54   $218.55   $218.50  
  Purchase #6 $214.83   4.374%   $224.2267   $224.23   $224.25   $224.20  
  Purchase #7 $14.45   11.585%   $16.124   $16.12   $16.10   $16.10  
  7 purchase totals = $960.27       $1,021.9548   $1,021.95   $1,021.90   $1,022.00