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	$23.89	8.253%	$25.8616	$25.86	$25.85	$25.90
Purchase #2	$222.31	7.250%	$238.4275	$238.43	$238.45	$238.40
Purchase #3	$249.47	5.670%	$263.6149	$263.61	$263.60	$263.60
Purchase #4	$53.56	9.511%	$58.6541	$58.65	$58.65	$58.70
Purchase #5	$191.47	13.178%	$216.7019	$216.70	$216.70	$216.70
Purchase #6	$105.40	7.399%	$113.1985	$113.20	$113.20	$113.20
Purchase #7	$73.61	12.362%	$82.7097	$82.71	$82.70	$82.70
7 purchase totals =	$919.71		$999.1682	$999.16	$999.15	$999.20