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	$7.59	6.489%	$8.0825	$8.08	$8.10	$8.10
Purchase #2	$113.88	12.306%	$127.8941	$127.89	$127.90	$127.90
Purchase #3	$109.38	4.363%	$114.1522	$114.15	$114.15	$114.20
Purchase #4	$69.31	4.603%	$72.5003	$72.50	$72.50	$72.50
Purchase #5	$138.68	7.156%	$148.6039	$148.60	$148.60	$148.60
Purchase #6	$81.60	12.404%	$91.7217	$91.72	$91.70	$91.70
Purchase #7	$17.33	8.279%	$18.7648	$18.76	$18.75	$18.80
7 purchase totals =	$537.77		$581.7195	$581.70	$581.70	$581.80