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	$125.33	11.607%	$139.8771	$139.88	$139.90	$139.90
Purchase #2	$84.33	13.376%	$95.61	$95.61	$95.60	$95.60
Purchase #3	$143.59	5.322%	$151.2319	$151.23	$151.25	$151.20
Purchase #4	$133.69	10.662%	$147.944	$147.94	$147.95	$147.90
Purchase #5	$120.42	4.721%	$126.105	$126.11	$126.10	$126.10
Purchase #6	$93.67	7.188%	$100.403	$100.40	$100.40	$100.40
Purchase #7	$19.28	10.125%	$21.2321	$21.23	$21.25	$21.20
7 purchase totals =	$720.31		$782.4031	$782.40	$782.45	$782.30