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	$190.88	10.500%	$210.9224	$210.92	$210.90	$210.90
Purchase #2	$47.89	8.451%	$51.9372	$51.94	$51.95	$51.90
Purchase #3	$34.33	8.614%	$37.2872	$37.29	$37.30	$37.30
Purchase #4	$116.40	6.420%	$123.8729	$123.87	$123.85	$123.90
Purchase #5	$83.31	9.472%	$91.2011	$91.20	$91.20	$91.20
Purchase #6	$211.80	6.445%	$225.4505	$225.45	$225.45	$225.50
Purchase #7	$123.52	5.176%	$129.9134	$129.91	$129.90	$129.90
7 purchase totals =	$808.13		$870.5847	$870.58	$870.55	$870.60