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 $177.63   5.376%   $187.1794   $187.18   $187.20   $187.20  
  Purchase #2 $65.63   4.742%   $68.7422   $68.74   $68.75   $68.70  
  Purchase #3 $239.72   9.812%   $263.2413   $263.24   $263.25   $263.20  
  Purchase #4 $26.39   13.728%   $30.0128   $30.01   $30.00   $30.00  
  Purchase #5 $231.77   4.512%   $242.2275   $242.23   $242.25   $242.20  
  Purchase #6 $132.99   3.463%   $137.5954   $137.60   $137.60   $137.60  
  Purchase #7 $90.53   5.199%   $95.2367   $95.24   $95.25   $95.20  
  7 purchase totals = $964.66       $1,024.2353   $1,024.24   $1,024.30   $1,024.10