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	$234.78	4.400%	$245.1103	$245.11	$245.10	$245.10
Purchase #2	$39.39	9.302%	$43.0541	$43.05	$43.05	$43.10
Purchase #3	$123.57	3.466%	$127.8529	$127.85	$127.85	$127.90
Purchase #4	$185.89	7.261%	$199.3875	$199.39	$199.40	$199.40
Purchase #5	$152.96	4.848%	$160.3755	$160.38	$160.40	$160.40
Purchase #6	$244.83	9.646%	$268.4463	$268.45	$268.45	$268.40
Purchase #7	$70.81	13.518%	$80.3821	$80.38	$80.40	$80.40
7 purchase totals =	$1,052.23		$1,124.6087	$1,124.61	$1,124.65	$1,124.70