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	$109.54	12.271%	$122.9817	$122.98	$123.00	$123.00
Purchase #2	$194.51	4.626%	$203.508	$203.51	$203.50	$203.50
Purchase #3	$112.86	3.108%	$116.3677	$116.37	$116.35	$116.40
Purchase #4	$84.85	8.501%	$92.0631	$92.06	$92.05	$92.10
Purchase #5	$83.27	8.355%	$90.2272	$90.23	$90.25	$90.20
Purchase #6	$205.43	4.461%	$214.5942	$214.59	$214.60	$214.60
Purchase #7	$96.27	7.619%	$103.6048	$103.60	$103.60	$103.60
7 purchase totals =	$886.73		$943.3467	$943.34	$943.35	$943.40