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	$120.91	5.568%	$127.6423	$127.64	$127.65	$127.60
Purchase #2	$109.60	10.673%	$121.2976	$121.30	$121.30	$121.30
Purchase #3	$217.71	12.562%	$245.0587	$245.06	$245.05	$245.10
Purchase #4	$142.59	5.109%	$149.8749	$149.87	$149.85	$149.90
Purchase #5	$45.44	13.322%	$51.4935	$51.49	$51.50	$51.50
Purchase #6	$167.93	12.658%	$189.1866	$189.19	$189.20	$189.20
Purchase #7	$109.30	13.341%	$123.8817	$123.88	$123.90	$123.90
7 purchase totals =	$913.48		$1,008.4353	$1,008.43	$1,008.45	$1,008.50