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	$30.49	7.526%	$32.7847	$32.78	$32.80	$32.80
Purchase #2	$57.45	3.828%	$59.6492	$59.65	$59.65	$59.60
Purchase #3	$138.82	4.799%	$145.482	$145.48	$145.50	$145.50
Purchase #4	$49.26	9.530%	$53.9545	$53.95	$53.95	$54.00
Purchase #5	$235.76	5.608%	$248.9814	$248.98	$249.00	$249.00
Purchase #6	$96.47	6.694%	$102.9277	$102.93	$102.95	$102.90
Purchase #7	$129.63	11.435%	$144.4532	$144.45	$144.45	$144.50
7 purchase totals =	$737.88		$788.2327	$788.22	$788.30	$788.30