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	$243.32	3.170%	$251.0332	$251.03	$251.05	$251.00
Purchase #2	$42.47	9.293%	$46.4167	$46.42	$46.40	$46.40
Purchase #3	$99.28	12.358%	$111.549	$111.55	$111.55	$111.50
Purchase #4	$185.96	10.377%	$205.2571	$205.26	$205.25	$205.30
Purchase #5	$197.81	4.278%	$206.2723	$206.27	$206.25	$206.30
Purchase #6	$131.66	12.831%	$148.5533	$148.55	$148.55	$148.60
Purchase #7	$22.45	12.572%	$25.2724	$25.27	$25.25	$25.30
7 purchase totals =	$922.95		$994.3540	$994.35	$994.30	$994.40