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	$250.84	12.596%	$282.4358	$282.44	$282.45	$282.40
Purchase #2	$69.91	9.655%	$76.6598	$76.66	$76.65	$76.70
Purchase #3	$227.81	9.327%	$249.0578	$249.06	$249.05	$249.10
Purchase #4	$89.32	13.664%	$101.5247	$101.52	$101.50	$101.50
Purchase #5	$173.29	7.684%	$186.6056	$186.61	$186.60	$186.60
Purchase #6	$213.92	9.120%	$233.4295	$233.43	$233.45	$233.40
Purchase #7	$37.32	13.812%	$42.4746	$42.47	$42.45	$42.50
7 purchase totals =	$1,062.41		$1,172.1878	$1,172.19	$1,172.15	$1,172.20