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 $233.26   8.697%   $253.5466   $253.55   $253.55   $253.50  
  Purchase #2 $27.55   9.747%   $30.2353   $30.24   $30.25   $30.20  
  Purchase #3 $236.77   12.865%   $267.2305   $267.23   $267.25   $267.20  
  Purchase #4 $121.83   5.582%   $128.6306   $128.63   $128.65   $128.60  
  Purchase #5 $134.95   7.598%   $145.2035   $145.20   $145.20   $145.20  
  Purchase #6 $164.60   6.358%   $175.0653   $175.07   $175.05   $175.10  
  Purchase #7 $25.99   5.649%   $27.4582   $27.46   $27.45   $27.50  
  7 purchase totals = $944.95       $1,027.3700   $1,027.38   $1,027.40   $1,027.30