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	$246.89	6.548%	$263.0564	$263.06	$263.05	$263.10
Purchase #2	$80.51	3.384%	$83.2345	$83.23	$83.25	$83.20
Purchase #3	$58.87	6.218%	$62.5305	$62.53	$62.55	$62.50
Purchase #4	$64.86	13.198%	$73.4202	$73.42	$73.40	$73.40
Purchase #5	$69.34	6.352%	$73.7445	$73.74	$73.75	$73.70
Purchase #6	$38.72	7.385%	$41.5795	$41.58	$41.60	$41.60
Purchase #7	$62.68	8.274%	$67.8661	$67.87	$67.85	$67.90
7 purchase totals =	$621.87		$665.4317	$665.43	$665.45	$665.40