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	$104.88	3.840%	$108.9074	$108.91	$108.90	$108.90
Purchase #2	$37.60	13.753%	$42.7711	$42.77	$42.75	$42.80
Purchase #3	$18.64	11.766%	$20.8332	$20.83	$20.85	$20.80
Purchase #4	$222.72	10.618%	$246.3684	$246.37	$246.35	$246.40
Purchase #5	$241.79	11.614%	$269.8715	$269.87	$269.85	$269.90
Purchase #6	$236.42	7.584%	$254.3501	$254.35	$254.35	$254.40
Purchase #7	$60.78	3.129%	$62.6818	$62.68	$62.70	$62.70
7 purchase totals =	$922.83		$1,005.7835	$1,005.78	$1,005.75	$1,005.90