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	$17.26	3.658%	$17.8914	$17.89	$17.90	$17.90
Purchase #2	$93.32	8.316%	$101.0805	$101.08	$101.10	$101.10
Purchase #3	$119.42	9.750%	$131.0635	$131.06	$131.05	$131.10
Purchase #4	$75.76	4.422%	$79.1101	$79.11	$79.10	$79.10
Purchase #5	$106.61	4.782%	$111.7081	$111.71	$111.70	$111.70
Purchase #6	$52.76	9.201%	$57.6144	$57.61	$57.60	$57.60
Purchase #7	$162.37	3.824%	$168.579	$168.58	$168.60	$168.60
7 purchase totals =	$627.50		$667.0470	$667.04	$667.05	$667.10