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	$126.25	13.172%	$142.8797	$142.88	$142.90	$142.90
Purchase #2	$195.38	6.412%	$207.9078	$207.91	$207.90	$207.90
Purchase #3	$51.25	9.485%	$56.1111	$56.11	$56.10	$56.10
Purchase #4	$80.31	12.449%	$90.3078	$90.31	$90.30	$90.30
Purchase #5	$175.82	9.411%	$192.3664	$192.37	$192.35	$192.40
Purchase #6	$40.93	11.616%	$45.6844	$45.68	$45.70	$45.70
Purchase #7	$135.46	9.722%	$148.6294	$148.63	$148.65	$148.60
7 purchase totals =	$805.40		$883.8866	$883.89	$883.90	$883.90