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	$65.99	12.826%	$74.4539	$74.45	$74.45	$74.50
Purchase #2	$82.68	8.741%	$89.9071	$89.91	$89.90	$89.90
Purchase #3	$157.91	10.225%	$174.0563	$174.06	$174.05	$174.10
Purchase #4	$80.80	13.563%	$91.7589	$91.76	$91.75	$91.80
Purchase #5	$110.83	5.238%	$116.6353	$116.64	$116.65	$116.60
Purchase #6	$39.61	13.617%	$45.0037	$45.00	$45.00	$45.00
Purchase #7	$131.49	9.314%	$143.737	$143.74	$143.75	$143.70
7 purchase totals =	$669.31		$735.5522	$735.56	$735.55	$735.60