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	$154.72	7.613%	$166.4988	$166.50	$166.50	$166.50
Purchase #2	$110.69	5.160%	$116.4016	$116.40	$116.40	$116.40
Purchase #3	$79.90	12.415%	$89.8196	$89.82	$89.80	$89.80
Purchase #4	$202.61	6.219%	$215.2103	$215.21	$215.20	$215.20
Purchase #5	$33.89	3.491%	$35.0731	$35.07	$35.05	$35.10
Purchase #6	$188.93	12.611%	$212.756	$212.76	$212.75	$212.80
Purchase #7	$139.46	9.552%	$152.7812	$152.78	$152.80	$152.80
7 purchase totals =	$910.20		$988.5406	$988.54	$988.50	$988.60