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	$130.32	13.123%	$147.4219	$147.42	$147.40	$147.40
Purchase #2	$159.49	7.313%	$171.1535	$171.15	$171.15	$171.20
Purchase #3	$230.71	3.399%	$238.5518	$238.55	$238.55	$238.60
Purchase #4	$65.75	7.669%	$70.7924	$70.79	$70.80	$70.80
Purchase #5	$70.77	11.495%	$78.905	$78.91	$78.90	$78.90
Purchase #6	$121.25	12.492%	$136.3966	$136.40	$136.40	$136.40
Purchase #7	$115.85	10.352%	$127.8428	$127.84	$127.85	$127.80
7 purchase totals =	$894.14		$971.0640	$971.06	$971.05	$971.10