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	$246.51	13.139%	$278.8989	$278.90	$278.90	$278.90
Purchase #2	$5.34	7.646%	$5.7483	$5.75	$5.75	$5.70
Purchase #3	$127.32	5.686%	$134.5594	$134.56	$134.55	$134.60
Purchase #4	$17.76	12.777%	$20.0292	$20.03	$20.05	$20.00
Purchase #5	$80.29	13.740%	$91.3218	$91.32	$91.30	$91.30
Purchase #6	$118.97	7.274%	$127.6239	$127.62	$127.60	$127.60
Purchase #7	$114.50	3.715%	$118.7537	$118.75	$118.75	$118.80
7 purchase totals =	$710.69		$776.9352	$776.93	$776.90	$776.90