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	$89.44	10.255%	$98.6121	$98.61	$98.60	$98.60
Purchase #2	$171.43	10.400%	$189.2587	$189.26	$189.25	$189.30
Purchase #3	$95.53	7.102%	$102.3145	$102.31	$102.30	$102.30
Purchase #4	$80.55	12.833%	$90.887	$90.89	$90.90	$90.90
Purchase #5	$32.38	8.489%	$35.1287	$35.13	$35.15	$35.10
Purchase #6	$77.27	12.182%	$86.683	$86.68	$86.70	$86.70
Purchase #7	$153.67	12.187%	$172.3978	$172.40	$172.40	$172.40
7 purchase totals =	$700.27		$775.2818	$775.28	$775.30	$775.30