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	$250.85	11.119%	$278.742	$278.74	$278.75	$278.70
Purchase #2	$50.74	4.379%	$52.9619	$52.96	$52.95	$53.00
Purchase #3	$199.59	13.324%	$226.1834	$226.18	$226.20	$226.20
Purchase #4	$245.86	10.814%	$272.4473	$272.45	$272.45	$272.40
Purchase #5	$80.52	3.619%	$83.434	$83.43	$83.45	$83.40
Purchase #6	$80.56	12.772%	$90.8491	$90.85	$90.85	$90.80
Purchase #7	$135.82	6.870%	$145.1508	$145.15	$145.15	$145.20
7 purchase totals =	$1,043.94		$1,149.7685	$1,149.76	$1,149.80	$1,149.70