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	$85.81	4.184%	$89.4003	$89.40	$89.40	$89.40
Purchase #2	$127.50	5.213%	$134.1466	$134.15	$134.15	$134.10
Purchase #3	$62.46	9.320%	$68.2813	$68.28	$68.30	$68.30
Purchase #4	$156.71	9.666%	$171.8576	$171.86	$171.85	$171.90
Purchase #5	$33.55	13.140%	$37.9585	$37.96	$37.95	$38.00
Purchase #6	$183.79	3.799%	$190.7722	$190.77	$190.75	$190.80
Purchase #7	$127.50	8.295%	$138.0761	$138.08	$138.10	$138.10
7 purchase totals =	$777.32		$830.4926	$830.50	$830.50	$830.60