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	$57.91	6.673%	$61.7743	$61.77	$61.75	$61.80
Purchase #2	$83.25	8.408%	$90.2497	$90.25	$90.25	$90.20
Purchase #3	$110.90	8.231%	$120.0282	$120.03	$120.05	$120.00
Purchase #4	$173.89	12.588%	$195.7793	$195.78	$195.80	$195.80
Purchase #5	$59.42	10.701%	$65.7785	$65.78	$65.80	$65.80
Purchase #6	$29.94	9.611%	$32.8175	$32.82	$32.80	$32.80
Purchase #7	$32.67	4.756%	$34.2238	$34.22	$34.20	$34.20
7 purchase totals =	$547.98		$600.6513	$600.65	$600.65	$600.60