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	$20.39	12.137%	$22.8647	$22.86	$22.85	$22.90
Purchase #2	$110.35	7.688%	$118.8337	$118.83	$118.85	$118.80
Purchase #3	$247.38	12.799%	$279.0422	$279.04	$279.05	$279.00
Purchase #4	$68.47	10.872%	$75.9141	$75.91	$75.90	$75.90
Purchase #5	$212.47	5.819%	$224.8336	$224.83	$224.85	$224.80
Purchase #6	$126.76	10.150%	$139.6261	$139.63	$139.65	$139.60
Purchase #7	$142.51	6.111%	$151.2188	$151.22	$151.20	$151.20
7 purchase totals =	$928.33		$1,012.3332	$1,012.32	$1,012.35	$1,012.20