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	$30.68	4.502%	$32.0612	$32.06	$32.05	$32.10
Purchase #2	$250.30	11.671%	$279.5125	$279.51	$279.50	$279.50
Purchase #3	$193.66	11.478%	$215.8883	$215.89	$215.90	$215.90
Purchase #4	$107.79	6.333%	$114.6163	$114.62	$114.60	$114.60
Purchase #5	$242.73	11.193%	$269.8988	$269.90	$269.90	$269.90
Purchase #6	$176.76	4.508%	$184.7283	$184.73	$184.75	$184.70
Purchase #7	$85.89	6.621%	$91.5768	$91.58	$91.60	$91.60
7 purchase totals =	$1,087.81		$1,188.2822	$1,188.29	$1,188.30	$1,188.30