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	$16.47	13.861%	$18.7529	$18.75	$18.75	$18.80
Purchase #2	$82.47	9.565%	$90.3583	$90.36	$90.35	$90.40
Purchase #3	$216.32	13.146%	$244.7574	$244.76	$244.75	$244.80
Purchase #4	$41.81	3.684%	$43.3503	$43.35	$43.35	$43.40
Purchase #5	$21.59	5.644%	$22.8085	$22.81	$22.80	$22.80
Purchase #6	$174.83	12.266%	$196.2746	$196.27	$196.25	$196.30
Purchase #7	$127.51	3.362%	$131.7969	$131.80	$131.80	$131.80
7 purchase totals =	$681.00		$748.0989	$748.10	$748.05	$748.30