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	$160.61	12.368%	$180.4742	$180.47	$180.45	$180.50
Purchase #2	$238.85	11.556%	$266.4515	$266.45	$266.45	$266.50
Purchase #3	$29.43	10.538%	$32.5313	$32.53	$32.55	$32.50
Purchase #4	$69.59	11.304%	$77.4565	$77.46	$77.45	$77.50
Purchase #5	$196.38	13.169%	$222.2413	$222.24	$222.25	$222.20
Purchase #6	$231.98	8.740%	$252.2551	$252.26	$252.25	$252.30
Purchase #7	$79.68	3.201%	$82.2306	$82.23	$82.25	$82.20
7 purchase totals =	$1,006.52		$1,113.6405	$1,113.64	$1,113.65	$1,113.70