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	$204.40	11.828%	$228.5764	$228.58	$228.60	$228.60
Purchase #2	$223.52	12.466%	$251.384	$251.38	$251.40	$251.40
Purchase #3	$126.39	13.847%	$143.8912	$143.89	$143.90	$143.90
Purchase #4	$134.60	3.737%	$139.63	$139.63	$139.65	$139.60
Purchase #5	$90.70	12.270%	$101.8289	$101.83	$101.85	$101.80
Purchase #6	$158.86	7.194%	$170.2884	$170.29	$170.30	$170.30
Purchase #7	$50.38	11.770%	$56.3097	$56.31	$56.30	$56.30
7 purchase totals =	$988.85		$1,091.9086	$1,091.91	$1,092.00	$1,091.90