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	$58.46	5.278%	$61.5455	$61.55	$61.55	$61.50
Purchase #2	$32.25	11.494%	$35.9568	$35.96	$35.95	$36.00
Purchase #3	$136.61	6.666%	$145.7164	$145.72	$145.70	$145.70
Purchase #4	$206.94	7.485%	$222.4295	$222.43	$222.45	$222.40
Purchase #5	$25.41	6.575%	$27.0807	$27.08	$27.10	$27.10
Purchase #6	$225.25	5.295%	$237.177	$237.18	$237.20	$237.20
Purchase #7	$82.89	10.490%	$91.5852	$91.59	$91.60	$91.60
7 purchase totals =	$767.81		$821.4911	$821.51	$821.55	$821.50