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	$25.48	10.135%	$28.0624	$28.06	$28.05	$28.10
Purchase #2	$104.61	6.547%	$111.4588	$111.46	$111.45	$111.50
Purchase #3	$167.26	4.233%	$174.3401	$174.34	$174.35	$174.30
Purchase #4	$145.42	6.467%	$154.8243	$154.82	$154.80	$154.80
Purchase #5	$59.40	3.224%	$61.3151	$61.32	$61.30	$61.30
Purchase #6	$248.89	9.560%	$272.6839	$272.68	$272.70	$272.70
Purchase #7	$208.53	13.534%	$236.7525	$236.75	$236.75	$236.80
7 purchase totals =	$959.59		$1,039.4371	$1,039.43	$1,039.40	$1,039.50