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	$91.73	11.538%	$102.3138	$102.31	$102.30	$102.30
Purchase #2	$236.81	13.774%	$269.4282	$269.43	$269.45	$269.40
Purchase #3	$240.32	6.323%	$255.5154	$255.52	$255.50	$255.50
Purchase #4	$83.25	13.467%	$94.4613	$94.46	$94.45	$94.50
Purchase #5	$95.43	9.598%	$104.5894	$104.59	$104.60	$104.60
Purchase #6	$99.73	10.650%	$110.3512	$110.35	$110.35	$110.40
Purchase #7	$122.43	12.251%	$137.4289	$137.43	$137.45	$137.40
7 purchase totals =	$969.70		$1,074.0882	$1,074.09	$1,074.10	$1,074.10