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	$59.98	11.116%	$66.6474	$66.65	$66.65	$66.60
Purchase #2	$63.30	12.472%	$71.1948	$71.19	$71.20	$71.20
Purchase #3	$247.52	9.305%	$270.5517	$270.55	$270.55	$270.60
Purchase #4	$206.72	3.463%	$213.8787	$213.88	$213.90	$213.90
Purchase #5	$86.75	3.635%	$89.9034	$89.90	$89.90	$89.90
Purchase #6	$90.62	5.324%	$95.4446	$95.44	$95.45	$95.40
Purchase #7	$85.47	7.290%	$91.7008	$91.70	$91.70	$91.70
7 purchase totals =	$840.36		$899.3214	$899.31	$899.35	$899.30