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	$93.84	6.318%	$99.7688	$99.77	$99.75	$99.80
Purchase #2	$241.92	5.842%	$256.053	$256.05	$256.05	$256.10
Purchase #3	$54.31	3.603%	$56.2668	$56.27	$56.25	$56.30
Purchase #4	$31.81	5.177%	$33.4568	$33.46	$33.45	$33.50
Purchase #5	$46.57	11.611%	$51.9772	$51.98	$52.00	$52.00
Purchase #6	$90.72	9.753%	$99.5679	$99.57	$99.55	$99.60
Purchase #7	$88.64	11.311%	$98.6661	$98.67	$98.65	$98.70
7 purchase totals =	$647.81		$695.7566	$695.77	$695.70	$696.00