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	$83.45	6.796%	$89.1213	$89.12	$89.10	$89.10
Purchase #2	$137.87	5.578%	$145.5604	$145.56	$145.55	$145.60
Purchase #3	$168.59	5.743%	$178.2721	$178.27	$178.25	$178.30
Purchase #4	$209.55	8.667%	$227.7117	$227.71	$227.70	$227.70
Purchase #5	$198.74	12.578%	$223.7375	$223.74	$223.75	$223.70
Purchase #6	$152.98	3.668%	$158.5913	$158.59	$158.60	$158.60
Purchase #7	$234.96	13.682%	$267.1072	$267.11	$267.10	$267.10
7 purchase totals =	$1,186.14		$1,290.1015	$1,290.10	$1,290.05	$1,290.10