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	$242.30	13.521%	$275.0614	$275.06	$275.05	$275.10
Purchase #2	$122.51	13.823%	$139.4446	$139.44	$139.45	$139.40
Purchase #3	$110.88	3.398%	$114.6477	$114.65	$114.65	$114.60
Purchase #4	$19.77	6.179%	$20.9916	$20.99	$21.00	$21.00
Purchase #5	$91.27	5.518%	$96.3063	$96.31	$96.30	$96.30
Purchase #6	$92.82	4.259%	$96.7732	$96.77	$96.75	$96.80
Purchase #7	$82.50	9.612%	$90.4299	$90.43	$90.45	$90.40
7 purchase totals =	$762.05		$833.6547	$833.65	$833.65	$833.60