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	$90.86	9.740%	$99.7098	$99.71	$99.70	$99.70
Purchase #2	$26.53	5.228%	$27.917	$27.92	$27.90	$27.90
Purchase #3	$158.86	13.637%	$180.5237	$180.52	$180.50	$180.50
Purchase #4	$47.78	4.259%	$49.815	$49.82	$49.80	$49.80
Purchase #5	$112.28	10.352%	$123.9032	$123.90	$123.90	$123.90
Purchase #6	$38.52	7.829%	$41.5357	$41.54	$41.55	$41.50
Purchase #7	$8.95	12.601%	$10.0778	$10.08	$10.10	$10.10
7 purchase totals =	$483.78		$533.4822	$533.49	$533.45	$533.40