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	$232.64	9.128%	$253.8754	$253.88	$253.90	$253.90
Purchase #2	$223.91	13.760%	$254.72	$254.72	$254.70	$254.70
Purchase #3	$80.90	10.239%	$89.1834	$89.18	$89.20	$89.20
Purchase #4	$102.46	13.582%	$116.3761	$116.38	$116.40	$116.40
Purchase #5	$170.25	3.329%	$175.9176	$175.92	$175.90	$175.90
Purchase #6	$227.32	3.262%	$234.7352	$234.74	$234.75	$234.70
Purchase #7	$77.87	10.153%	$85.7761	$85.78	$85.80	$85.80
7 purchase totals =	$1,115.35		$1,210.5838	$1,210.60	$1,210.65	$1,210.60