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	$90.74	8.706%	$98.6398	$98.64	$98.65	$98.60
Purchase #2	$217.55	4.731%	$227.8423	$227.84	$227.85	$227.80
Purchase #3	$95.30	6.422%	$101.4202	$101.42	$101.40	$101.40
Purchase #4	$6.94	5.564%	$7.3261	$7.33	$7.35	$7.30
Purchase #5	$53.85	10.403%	$59.452	$59.45	$59.45	$59.50
Purchase #6	$12.58	4.229%	$13.112	$13.11	$13.10	$13.10
Purchase #7	$126.76	4.717%	$132.7393	$132.74	$132.75	$132.70
7 purchase totals =	$603.72		$640.5317	$640.53	$640.55	$640.40