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	$92.59	8.798%	$100.7361	$100.74	$100.75	$100.70
Purchase #2	$151.58	13.584%	$172.1706	$172.17	$172.15	$172.20
Purchase #3	$79.63	12.740%	$89.7749	$89.77	$89.75	$89.80
Purchase #4	$120.59	6.566%	$128.5079	$128.51	$128.50	$128.50
Purchase #5	$82.44	13.637%	$93.6823	$93.68	$93.70	$93.70
Purchase #6	$56.74	8.385%	$61.4976	$61.50	$61.50	$61.50
Purchase #7	$164.47	7.263%	$176.4155	$176.42	$176.40	$176.40
7 purchase totals =	$748.04		$822.7849	$822.79	$822.75	$822.80