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	$82.92	9.792%	$91.0395	$91.04	$91.05	$91.00
Purchase #2	$179.69	8.115%	$194.2718	$194.27	$194.25	$194.30
Purchase #3	$91.36	8.656%	$99.2681	$99.27	$99.25	$99.30
Purchase #4	$233.42	3.711%	$242.0822	$242.08	$242.10	$242.10
Purchase #5	$214.53	11.372%	$238.9264	$238.93	$238.95	$238.90
Purchase #6	$12.67	12.268%	$14.2244	$14.22	$14.20	$14.20
Purchase #7	$92.81	12.189%	$104.1226	$104.12	$104.10	$104.10
7 purchase totals =	$907.40		$983.9350	$983.93	$983.90	$983.90