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	$205.60	8.212%	$222.4839	$222.48	$222.50	$222.50
Purchase #2	$182.76	5.112%	$192.1027	$192.10	$192.10	$192.10
Purchase #3	$115.67	10.147%	$127.407	$127.41	$127.40	$127.40
Purchase #4	$229.99	12.638%	$259.0561	$259.06	$259.05	$259.10
Purchase #5	$185.83	8.121%	$200.9213	$200.92	$200.90	$200.90
Purchase #6	$130.65	11.322%	$145.4422	$145.44	$145.45	$145.40
Purchase #7	$142.65	11.112%	$158.5013	$158.50	$158.50	$158.50
7 purchase totals =	$1,193.15		$1,305.9145	$1,305.91	$1,305.90	$1,305.90