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	$44.62	13.502%	$50.6446	$50.64	$50.65	$50.60
Purchase #2	$29.77	12.571%	$33.5124	$33.51	$33.50	$33.50
Purchase #3	$84.86	5.722%	$89.7157	$89.72	$89.70	$89.70
Purchase #4	$36.27	10.550%	$40.0965	$40.10	$40.10	$40.10
Purchase #5	$141.56	5.174%	$148.8843	$148.88	$148.90	$148.90
Purchase #6	$93.92	4.563%	$98.2056	$98.21	$98.20	$98.20
Purchase #7	$158.80	6.597%	$169.276	$169.28	$169.30	$169.30
7 purchase totals =	$589.80		$630.3351	$630.34	$630.35	$630.30