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	$228.60	6.506%	$243.4727	$243.47	$243.45	$243.50
Purchase #2	$244.68	5.804%	$258.8812	$258.88	$258.90	$258.90
Purchase #3	$50.90	4.133%	$53.0037	$53.00	$53.00	$53.00
Purchase #4	$74.92	11.570%	$83.5882	$83.59	$83.60	$83.60
Purchase #5	$149.58	4.343%	$156.0763	$156.08	$156.10	$156.10
Purchase #6	$185.71	10.113%	$204.4909	$204.49	$204.50	$204.50
Purchase #7	$12.30	6.165%	$13.0583	$13.06	$13.05	$13.10
7 purchase totals =	$946.69		$1,012.5713	$1,012.57	$1,012.60	$1,012.70