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	$52.82	13.258%	$59.8229	$59.82	$59.80	$59.80
Purchase #2	$100.55	9.201%	$109.8016	$109.80	$109.80	$109.80
Purchase #3	$209.65	5.364%	$220.8956	$220.90	$220.90	$220.90
Purchase #4	$45.66	12.795%	$51.5022	$51.50	$51.50	$51.50
Purchase #5	$105.41	12.740%	$118.8392	$118.84	$118.85	$118.80
Purchase #6	$235.52	6.651%	$251.1844	$251.18	$251.20	$251.20
Purchase #7	$99.77	8.818%	$108.5677	$108.57	$108.55	$108.60
7 purchase totals =	$849.38		$920.6136	$920.61	$920.60	$920.60