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	$30.28	5.161%	$31.8428	$31.84	$31.85	$31.80
Purchase #2	$160.93	4.568%	$168.2813	$168.28	$168.30	$168.30
Purchase #3	$123.28	13.763%	$140.247	$140.25	$140.25	$140.20
Purchase #4	$143.52	10.612%	$158.7503	$158.75	$158.75	$158.80
Purchase #5	$209.43	13.314%	$237.3135	$237.31	$237.30	$237.30
Purchase #6	$147.72	7.447%	$158.7207	$158.72	$158.70	$158.70
Purchase #7	$127.70	11.278%	$142.102	$142.10	$142.10	$142.10
7 purchase totals =	$942.86		$1,037.2576	$1,037.25	$1,037.25	$1,037.20