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	$226.76	9.562%	$248.4428	$248.44	$248.45	$248.40
Purchase #2	$172.89	10.178%	$190.4867	$190.49	$190.50	$190.50
Purchase #3	$209.77	4.429%	$219.0607	$219.06	$219.05	$219.10
Purchase #4	$141.76	4.794%	$148.556	$148.56	$148.55	$148.60
Purchase #5	$88.62	12.433%	$99.6381	$99.64	$99.65	$99.60
Purchase #6	$170.96	13.664%	$194.32	$194.32	$194.30	$194.30
Purchase #7	$166.36	8.463%	$180.439	$180.44	$180.45	$180.40
7 purchase totals =	$1,177.12		$1,280.9433	$1,280.95	$1,280.95	$1,280.90