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	$202.47	9.761%	$222.2331	$222.23	$222.25	$222.20
Purchase #2	$220.99	3.847%	$229.4915	$229.49	$229.50	$229.50
Purchase #3	$144.44	9.779%	$158.5648	$158.56	$158.55	$158.60
Purchase #4	$129.89	5.403%	$136.908	$136.91	$136.90	$136.90
Purchase #5	$18.36	9.464%	$20.0976	$20.10	$20.10	$20.10
Purchase #6	$53.64	8.640%	$58.2745	$58.27	$58.25	$58.30
Purchase #7	$119.52	9.865%	$131.3106	$131.31	$131.30	$131.30
7 purchase totals =	$889.31		$956.8801	$956.87	$956.85	$956.90