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	$81.30	10.810%	$90.0885	$90.09	$90.10	$90.10
Purchase #2	$215.73	11.114%	$239.7062	$239.71	$239.70	$239.70
Purchase #3	$124.61	12.318%	$139.9595	$139.96	$139.95	$140.00
Purchase #4	$235.73	3.440%	$243.8391	$243.84	$243.85	$243.80
Purchase #5	$63.72	4.501%	$66.588	$66.59	$66.60	$66.60
Purchase #6	$114.67	11.255%	$127.5761	$127.58	$127.60	$127.60
Purchase #7	$101.55	10.274%	$111.9832	$111.98	$112.00	$112.00
7 purchase totals =	$937.31		$1,019.7406	$1,019.75	$1,019.80	$1,019.80