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	$93.60	12.816%	$105.5958	$105.60	$105.60	$105.60
Purchase #2	$171.40	6.367%	$182.313	$182.31	$182.30	$182.30
Purchase #3	$232.39	10.477%	$256.7375	$256.74	$256.75	$256.70
Purchase #4	$226.97	12.689%	$255.7702	$255.77	$255.75	$255.80
Purchase #5	$6.26	5.655%	$6.614	$6.61	$6.60	$6.60
Purchase #6	$86.70	11.415%	$96.5968	$96.60	$96.60	$96.60
Purchase #7	$180.42	10.584%	$199.5157	$199.52	$199.50	$199.50
7 purchase totals =	$997.74		$1,103.1430	$1,103.15	$1,103.10	$1,103.10