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	$244.73	4.747%	$256.3473	$256.35	$256.35	$256.30
Purchase #2	$54.66	9.469%	$59.8358	$59.84	$59.85	$59.80
Purchase #3	$74.59	7.518%	$80.1977	$80.20	$80.20	$80.20
Purchase #4	$247.72	13.222%	$280.4735	$280.47	$280.45	$280.50
Purchase #5	$250.38	4.145%	$260.7583	$260.76	$260.75	$260.80
Purchase #6	$19.86	12.576%	$22.3576	$22.36	$22.35	$22.40
Purchase #7	$115.45	12.269%	$129.6146	$129.61	$129.60	$129.60
7 purchase totals =	$1,007.39		$1,089.5848	$1,089.59	$1,089.55	$1,089.60