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	$118.30	3.665%	$122.6357	$122.64	$122.65	$122.60
Purchase #2	$139.28	8.343%	$150.9001	$150.90	$150.90	$150.90
Purchase #3	$145.88	13.627%	$165.7591	$165.76	$165.75	$165.80
Purchase #4	$54.40	8.592%	$59.074	$59.07	$59.05	$59.10
Purchase #5	$42.79	11.727%	$47.808	$47.81	$47.80	$47.80
Purchase #6	$235.27	9.446%	$257.4936	$257.49	$257.50	$257.50
Purchase #7	$52.62	8.115%	$56.8901	$56.89	$56.90	$56.90
7 purchase totals =	$788.54		$860.5606	$860.56	$860.55	$860.60