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	$27.64	4.670%	$28.9308	$28.93	$28.95	$28.90
Purchase #2	$172.49	10.512%	$190.6221	$190.62	$190.60	$190.60
Purchase #3	$19.25	6.120%	$20.4281	$20.43	$20.45	$20.40
Purchase #4	$122.62	6.237%	$130.2678	$130.27	$130.25	$130.30
Purchase #5	$67.60	6.713%	$72.138	$72.14	$72.15	$72.10
Purchase #6	$112.38	11.587%	$125.4015	$125.40	$125.40	$125.40
Purchase #7	$222.54	8.170%	$240.7215	$240.72	$240.70	$240.70
7 purchase totals =	$744.52		$808.5098	$808.51	$808.50	$808.40