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	$28.27	6.737%	$30.1745	$30.17	$30.15	$30.20
Purchase #2	$11.92	13.123%	$13.4843	$13.48	$13.50	$13.50
Purchase #3	$39.60	6.139%	$42.031	$42.03	$42.05	$42.00
Purchase #4	$148.66	12.415%	$167.1161	$167.12	$167.10	$167.10
Purchase #5	$50.99	4.177%	$53.1199	$53.12	$53.10	$53.10
Purchase #6	$151.67	10.147%	$167.06	$167.06	$167.05	$167.10
Purchase #7	$94.82	8.817%	$103.1803	$103.18	$103.20	$103.20
7 purchase totals =	$525.93		$576.1661	$576.16	$576.15	$576.20