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	$105.93	13.429%	$120.1553	$120.16	$120.15	$120.20
Purchase #2	$51.57	3.562%	$53.4069	$53.41	$53.40	$53.40
Purchase #3	$83.83	3.375%	$86.6593	$86.66	$86.65	$86.70
Purchase #4	$127.97	5.350%	$134.8164	$134.82	$134.80	$134.80
Purchase #5	$49.93	9.585%	$54.7158	$54.72	$54.70	$54.70
Purchase #6	$72.85	7.456%	$78.2817	$78.28	$78.30	$78.30
Purchase #7	$36.98	3.660%	$38.3335	$38.33	$38.35	$38.30
7 purchase totals =	$529.06		$566.3689	$566.38	$566.35	$566.40