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	$180.83	10.497%	$199.8117	$199.81	$199.80	$199.80
Purchase #2	$112.77	13.775%	$128.3041	$128.30	$128.30	$128.30
Purchase #3	$167.61	11.829%	$187.4366	$187.44	$187.45	$187.40
Purchase #4	$102.84	8.196%	$111.2688	$111.27	$111.25	$111.30
Purchase #5	$107.38	8.662%	$116.6813	$116.68	$116.70	$116.70
Purchase #6	$217.32	10.591%	$240.3364	$240.34	$240.35	$240.30
Purchase #7	$90.74	6.799%	$96.9094	$96.91	$96.90	$96.90
7 purchase totals =	$979.49		$1,080.7483	$1,080.75	$1,080.75	$1,080.70