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	$235.49	8.397%	$255.2641	$255.26	$255.25	$255.30
Purchase #2	$24.64	9.761%	$27.0451	$27.05	$27.05	$27.00
Purchase #3	$191.76	4.521%	$200.4295	$200.43	$200.45	$200.40
Purchase #4	$7.92	6.380%	$8.4253	$8.43	$8.45	$8.40
Purchase #5	$183.60	7.108%	$196.6503	$196.65	$196.65	$196.70
Purchase #6	$225.77	8.479%	$244.913	$244.91	$244.90	$244.90
Purchase #7	$24.68	12.694%	$27.8129	$27.81	$27.80	$27.80
7 purchase totals =	$893.86		$960.5402	$960.54	$960.55	$960.50