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	$104.35	6.269%	$110.8917	$110.89	$110.90	$110.90
Purchase #2	$186.87	13.119%	$211.3855	$211.39	$211.40	$211.40
Purchase #3	$132.56	10.250%	$146.1474	$146.15	$146.15	$146.10
Purchase #4	$69.36	12.648%	$78.1327	$78.13	$78.15	$78.10
Purchase #5	$9.78	12.335%	$10.9864	$10.99	$11.00	$11.00
Purchase #6	$5.63	4.600%	$5.889	$5.89	$5.90	$5.90
Purchase #7	$10.47	3.625%	$10.8495	$10.85	$10.85	$10.80
7 purchase totals =	$519.02		$574.2822	$574.29	$574.35	$574.20