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	$199.75	10.293%	$220.3103	$220.31	$220.30	$220.30
Purchase #2	$10.31	10.470%	$11.3895	$11.39	$11.40	$11.40
Purchase #3	$124.28	6.453%	$132.2998	$132.30	$132.30	$132.30
Purchase #4	$104.40	6.619%	$111.3102	$111.31	$111.30	$111.30
Purchase #5	$45.47	12.242%	$51.0364	$51.04	$51.05	$51.00
Purchase #6	$58.67	12.707%	$66.1252	$66.13	$66.15	$66.10
Purchase #7	$182.94	4.851%	$191.8144	$191.81	$191.80	$191.80
7 purchase totals =	$725.82		$784.2858	$784.29	$784.30	$784.20