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	$12.77	5.383%	$13.4574	$13.46	$13.45	$13.50
Purchase #2	$199.51	11.749%	$222.9504	$222.95	$222.95	$223.00
Purchase #3	$145.96	12.798%	$164.64	$164.64	$164.65	$164.60
Purchase #4	$170.69	13.818%	$194.2759	$194.28	$194.30	$194.30
Purchase #5	$18.76	7.258%	$20.1216	$20.12	$20.10	$20.10
Purchase #6	$176.82	13.316%	$200.3654	$200.37	$200.35	$200.40
Purchase #7	$69.66	7.353%	$74.7821	$74.78	$74.80	$74.80
7 purchase totals =	$794.17		$890.5928	$890.60	$890.60	$890.70