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	$200.87	12.847%	$226.6758	$226.68	$226.70	$226.70
Purchase #2	$28.62	12.832%	$32.2925	$32.29	$32.30	$32.30
Purchase #3	$225.56	3.722%	$233.9553	$233.96	$233.95	$234.00
Purchase #4	$43.52	7.610%	$46.8319	$46.83	$46.85	$46.80
Purchase #5	$128.33	9.485%	$140.5021	$140.50	$140.50	$140.50
Purchase #6	$33.49	10.687%	$37.0691	$37.07	$37.05	$37.10
Purchase #7	$214.39	3.617%	$222.1445	$222.14	$222.15	$222.10
7 purchase totals =	$874.78		$939.4712	$939.47	$939.50	$939.50