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	$241.86	7.434%	$259.8399	$259.84	$259.85	$259.80
Purchase #2	$98.98	12.523%	$111.3753	$111.38	$111.40	$111.40
Purchase #3	$104.82	6.722%	$111.866	$111.87	$111.85	$111.90
Purchase #4	$183.40	9.466%	$200.7606	$200.76	$200.75	$200.80
Purchase #5	$243.56	12.544%	$274.1122	$274.11	$274.10	$274.10
Purchase #6	$120.73	3.794%	$125.3105	$125.31	$125.30	$125.30
Purchase #7	$13.89	6.276%	$14.7617	$14.76	$14.75	$14.80
7 purchase totals =	$1,007.24		$1,098.0262	$1,098.03	$1,098.00	$1,098.10