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	$99.77	11.762%	$111.5049	$111.50	$111.50	$111.50
Purchase #2	$227.89	8.543%	$247.3586	$247.36	$247.35	$247.40
Purchase #3	$35.91	11.588%	$40.0713	$40.07	$40.05	$40.10
Purchase #4	$171.42	8.145%	$185.3822	$185.38	$185.40	$185.40
Purchase #5	$235.45	10.730%	$260.7138	$260.71	$260.70	$260.70
Purchase #6	$219.99	3.459%	$227.5995	$227.60	$227.60	$227.60
Purchase #7	$70.46	5.607%	$74.4107	$74.41	$74.40	$74.40
7 purchase totals =	$1,060.89		$1,147.0410	$1,147.03	$1,147.00	$1,147.10