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	$230.43	9.169%	$251.5581	$251.56	$251.55	$251.60
Purchase #2	$163.63	5.672%	$172.9111	$172.91	$172.90	$172.90
Purchase #3	$241.37	11.378%	$268.8331	$268.83	$268.85	$268.80
Purchase #4	$86.78	9.152%	$94.7221	$94.72	$94.70	$94.70
Purchase #5	$48.38	3.835%	$50.2354	$50.24	$50.25	$50.20
Purchase #6	$142.30	6.765%	$151.9266	$151.93	$151.95	$151.90
Purchase #7	$79.67	8.770%	$86.6571	$86.66	$86.65	$86.70
7 purchase totals =	$992.56		$1,076.8435	$1,076.85	$1,076.85	$1,076.80