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	$143.91	10.160%	$158.5313	$158.53	$158.55	$158.50
Purchase #2	$17.52	4.299%	$18.2732	$18.27	$18.25	$18.30
Purchase #3	$125.38	12.874%	$141.5214	$141.52	$141.50	$141.50
Purchase #4	$217.88	10.638%	$241.0581	$241.06	$241.05	$241.10
Purchase #5	$137.31	9.229%	$149.9823	$149.98	$150.00	$150.00
Purchase #6	$171.37	11.343%	$190.8085	$190.81	$190.80	$190.80
Purchase #7	$20.58	10.606%	$22.7627	$22.76	$22.75	$22.80
7 purchase totals =	$833.95		$922.9375	$922.93	$922.90	$923.00