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	$78.77	13.665%	$89.5339	$89.53	$89.55	$89.50
Purchase #2	$9.62	5.777%	$10.1757	$10.18	$10.20	$10.20
Purchase #3	$105.32	4.152%	$109.6929	$109.69	$109.70	$109.70
Purchase #4	$111.71	11.669%	$124.7454	$124.75	$124.75	$124.70
Purchase #5	$42.33	7.238%	$45.3938	$45.39	$45.40	$45.40
Purchase #6	$27.45	4.461%	$28.6745	$28.67	$28.65	$28.70
Purchase #7	$215.30	3.764%	$223.4039	$223.40	$223.40	$223.40
7 purchase totals =	$590.50		$631.6201	$631.61	$631.65	$631.60