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	$243.53	6.550%	$259.4812	$259.48	$259.50	$259.50
Purchase #2	$168.74	7.678%	$181.6959	$181.70	$181.70	$181.70
Purchase #3	$72.68	8.657%	$78.9719	$78.97	$78.95	$79.00
Purchase #4	$35.79	9.845%	$39.3135	$39.31	$39.30	$39.30
Purchase #5	$172.99	7.156%	$185.3692	$185.37	$185.35	$185.40
Purchase #6	$25.27	13.170%	$28.5981	$28.60	$28.60	$28.60
Purchase #7	$42.42	10.386%	$46.8257	$46.83	$46.85	$46.80
7 purchase totals =	$761.42		$820.2555	$820.26	$820.25	$820.30