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	$43.72	5.500%	$46.1246	$46.12	$46.10	$46.10
Purchase #2	$57.31	7.765%	$61.7601	$61.76	$61.75	$61.80
Purchase #3	$207.70	7.674%	$223.6389	$223.64	$223.65	$223.60
Purchase #4	$7.54	13.749%	$8.5767	$8.58	$8.60	$8.60
Purchase #5	$122.81	7.174%	$131.6204	$131.62	$131.60	$131.60
Purchase #6	$127.40	6.596%	$135.8033	$135.80	$135.80	$135.80
Purchase #7	$28.47	13.490%	$32.3106	$32.31	$32.30	$32.30
7 purchase totals =	$594.95		$639.8346	$639.83	$639.80	$639.80