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	$108.39	13.508%	$123.0313	$123.03	$123.05	$123.00
Purchase #2	$46.70	6.800%	$49.8756	$49.88	$49.90	$49.90
Purchase #3	$169.63	9.156%	$185.1613	$185.16	$185.15	$185.20
Purchase #4	$243.59	10.612%	$269.4398	$269.44	$269.45	$269.40
Purchase #5	$67.97	9.122%	$74.1702	$74.17	$74.15	$74.20
Purchase #6	$89.63	11.622%	$100.0468	$100.05	$100.05	$100.00
Purchase #7	$89.68	5.290%	$94.4241	$94.42	$94.40	$94.40
7 purchase totals =	$815.59		$896.1491	$896.15	$896.15	$896.10