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	$81.91	4.427%	$85.5362	$85.54	$85.55	$85.50
Purchase #2	$161.56	13.463%	$183.3108	$183.31	$183.30	$183.30
Purchase #3	$166.83	4.534%	$174.3941	$174.39	$174.40	$174.40
Purchase #4	$32.33	10.145%	$35.6099	$35.61	$35.60	$35.60
Purchase #5	$127.30	13.685%	$144.721	$144.72	$144.70	$144.70
Purchase #6	$70.80	4.847%	$74.2317	$74.23	$74.25	$74.20
Purchase #7	$40.30	5.872%	$42.6664	$42.67	$42.65	$42.70
7 purchase totals =	$681.03		$740.4701	$740.47	$740.45	$740.40