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	$235.34	6.585%	$250.8371	$250.84	$250.85	$250.80
Purchase #2	$92.91	3.399%	$96.068	$96.07	$96.05	$96.10
Purchase #3	$136.47	13.212%	$154.5004	$154.50	$154.50	$154.50
Purchase #4	$131.43	6.156%	$139.5208	$139.52	$139.50	$139.50
Purchase #5	$157.42	4.574%	$164.6204	$164.62	$164.60	$164.60
Purchase #6	$73.30	8.536%	$79.5569	$79.56	$79.55	$79.60
Purchase #7	$243.31	6.367%	$258.8015	$258.80	$258.80	$258.80
7 purchase totals =	$1,070.18		$1,143.9051	$1,143.91	$1,143.85	$1,143.90