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	$154.76	11.463%	$172.5001	$172.50	$172.50	$172.50
Purchase #2	$197.99	7.365%	$212.572	$212.57	$212.55	$212.60
Purchase #3	$84.89	5.449%	$89.5157	$89.52	$89.50	$89.50
Purchase #4	$151.42	13.648%	$172.0858	$172.09	$172.10	$172.10
Purchase #5	$47.56	3.143%	$49.0548	$49.05	$49.05	$49.10
Purchase #6	$190.78	8.250%	$206.5194	$206.52	$206.50	$206.50
Purchase #7	$33.81	4.628%	$35.3747	$35.37	$35.35	$35.40
7 purchase totals =	$861.21		$937.6225	$937.62	$937.55	$937.70