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	$114.61	12.255%	$128.6555	$128.66	$128.65	$128.70
Purchase #2	$124.25	12.549%	$139.8421	$139.84	$139.85	$139.80
Purchase #3	$90.90	8.765%	$98.8674	$98.87	$98.85	$98.90
Purchase #4	$105.94	12.486%	$119.1677	$119.17	$119.15	$119.20
Purchase #5	$75.47	4.497%	$78.8639	$78.86	$78.85	$78.90
Purchase #6	$91.29	7.203%	$97.8656	$97.87	$97.85	$97.90
Purchase #7	$145.43	6.843%	$155.3818	$155.38	$155.40	$155.40
7 purchase totals =	$747.89		$818.6440	$818.65	$818.60	$818.80