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	$249.83	9.507%	$273.5813	$273.58	$273.60	$273.60
Purchase #2	$10.29	7.301%	$11.0413	$11.04	$11.05	$11.00
Purchase #3	$183.39	4.439%	$191.5307	$191.53	$191.55	$191.50
Purchase #4	$146.71	4.710%	$153.62	$153.62	$153.60	$153.60
Purchase #5	$127.52	9.368%	$139.4661	$139.47	$139.45	$139.50
Purchase #6	$19.80	5.304%	$20.8502	$20.85	$20.85	$20.90
Purchase #7	$100.29	12.798%	$113.1251	$113.13	$113.15	$113.10
7 purchase totals =	$837.83		$903.2147	$903.22	$903.25	$903.20