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	$77.53	4.124%	$80.7273	$80.73	$80.75	$80.70
Purchase #2	$39.88	7.862%	$43.0154	$43.02	$43.00	$43.00
Purchase #3	$100.94	11.449%	$112.4966	$112.50	$112.50	$112.50
Purchase #4	$149.46	11.448%	$166.5702	$166.57	$166.55	$166.60
Purchase #5	$241.59	10.400%	$266.7154	$266.72	$266.70	$266.70
Purchase #6	$110.66	7.177%	$118.6021	$118.60	$118.60	$118.60
Purchase #7	$20.37	10.191%	$22.4459	$22.45	$22.45	$22.40
7 purchase totals =	$740.43		$810.5729	$810.59	$810.55	$810.50