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	$124.43	13.539%	$141.2766	$141.28	$141.30	$141.30
Purchase #2	$120.66	13.126%	$136.4978	$136.50	$136.50	$136.50
Purchase #3	$240.41	9.343%	$262.8715	$262.87	$262.85	$262.90
Purchase #4	$15.39	4.633%	$16.103	$16.10	$16.10	$16.10
Purchase #5	$78.85	13.505%	$89.4987	$89.50	$89.50	$89.50
Purchase #6	$40.64	6.736%	$43.3775	$43.38	$43.40	$43.40
Purchase #7	$42.65	6.163%	$45.2785	$45.28	$45.30	$45.30
7 purchase totals =	$663.03		$734.9036	$734.91	$734.95	$735.00