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	$70.44	8.600%	$76.4978	$76.50	$76.50	$76.50
Purchase #2	$68.72	7.227%	$73.6864	$73.69	$73.70	$73.70
Purchase #3	$231.72	3.111%	$238.9288	$238.93	$238.95	$238.90
Purchase #4	$205.77	9.744%	$225.8202	$225.82	$225.80	$225.80
Purchase #5	$12.61	9.418%	$13.7976	$13.80	$13.80	$13.80
Purchase #6	$154.70	10.711%	$171.2699	$171.27	$171.25	$171.30
Purchase #7	$40.43	9.514%	$44.2765	$44.28	$44.30	$44.30
7 purchase totals =	$784.39		$844.2772	$844.29	$844.30	$844.30