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	$19.86	11.357%	$22.1155	$22.12	$22.10	$22.10
Purchase #2	$242.52	6.406%	$258.0558	$258.06	$258.05	$258.10
Purchase #3	$218.28	4.208%	$227.4652	$227.47	$227.45	$227.50
Purchase #4	$107.34	4.228%	$111.8783	$111.88	$111.90	$111.90
Purchase #5	$36.60	9.465%	$40.0642	$40.06	$40.05	$40.10
Purchase #6	$233.39	13.477%	$264.844	$264.84	$264.85	$264.80
Purchase #7	$29.95	12.675%	$33.7462	$33.75	$33.75	$33.70
7 purchase totals =	$887.94		$958.1692	$958.18	$958.15	$958.20