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	$113.62	11.859%	$127.0942	$127.09	$127.10	$127.10
Purchase #2	$248.70	6.328%	$264.4377	$264.44	$264.45	$264.40
Purchase #3	$122.42	7.734%	$131.888	$131.89	$131.90	$131.90
Purchase #4	$27.76	6.773%	$29.6402	$29.64	$29.65	$29.60
Purchase #5	$212.94	9.149%	$232.4219	$232.42	$232.40	$232.40
Purchase #6	$41.97	10.380%	$46.3265	$46.33	$46.35	$46.30
Purchase #7	$87.60	3.679%	$90.8228	$90.82	$90.80	$90.80
7 purchase totals =	$855.01		$922.6313	$922.63	$922.65	$922.50