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	$26.95	6.114%	$28.5977	$28.60	$28.60	$28.60
Purchase #2	$189.68	13.809%	$215.8729	$215.87	$215.85	$215.90
Purchase #3	$201.30	10.301%	$222.0359	$222.04	$222.05	$222.00
Purchase #4	$32.99	7.757%	$35.549	$35.55	$35.55	$35.50
Purchase #5	$82.89	8.574%	$89.997	$90.00	$90.00	$90.00
Purchase #6	$11.61	6.376%	$12.3503	$12.35	$12.35	$12.40
Purchase #7	$123.65	6.237%	$131.3621	$131.36	$131.35	$131.40
7 purchase totals =	$669.07		$735.7649	$735.77	$735.75	$735.80