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	$31.75	4.831%	$33.2838	$33.28	$33.30	$33.30
Purchase #2	$42.51	10.705%	$47.0607	$47.06	$47.05	$47.10
Purchase #3	$179.69	8.521%	$195.0014	$195.00	$195.00	$195.00
Purchase #4	$112.83	13.174%	$127.6942	$127.69	$127.70	$127.70
Purchase #5	$229.97	8.741%	$250.0717	$250.07	$250.05	$250.10
Purchase #6	$220.80	6.461%	$235.0659	$235.07	$235.05	$235.10
Purchase #7	$79.42	13.746%	$90.3371	$90.34	$90.35	$90.30
7 purchase totals =	$896.97		$978.5148	$978.51	$978.50	$978.60