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	$73.45	7.344%	$78.8442	$78.84	$78.85	$78.80
Purchase #2	$99.38	13.377%	$112.6741	$112.67	$112.65	$112.70
Purchase #3	$148.31	4.806%	$155.4378	$155.44	$155.45	$155.40
Purchase #4	$172.82	6.601%	$184.2278	$184.23	$184.25	$184.20
Purchase #5	$135.83	4.104%	$141.4045	$141.40	$141.40	$141.40
Purchase #6	$42.97	8.145%	$46.4699	$46.47	$46.45	$46.50
Purchase #7	$227.75	7.382%	$244.5625	$244.56	$244.55	$244.60
7 purchase totals =	$900.51		$963.6208	$963.61	$963.60	$963.60