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	$158.59	13.500%	$179.9997	$180.00	$180.00	$180.00
Purchase #2	$85.91	4.252%	$89.5629	$89.56	$89.55	$89.60
Purchase #3	$109.72	10.755%	$121.5204	$121.52	$121.50	$121.50
Purchase #4	$51.61	4.579%	$53.9732	$53.97	$53.95	$54.00
Purchase #5	$124.98	5.182%	$131.4565	$131.46	$131.45	$131.50
Purchase #6	$46.43	11.559%	$51.7968	$51.80	$51.80	$51.80
Purchase #7	$210.48	9.163%	$229.7663	$229.77	$229.75	$229.80
7 purchase totals =	$787.72		$858.0758	$858.08	$858.00	$858.20