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	$136.27	8.769%	$148.2195	$148.22	$148.20	$148.20
Purchase #2	$35.83	4.495%	$37.4406	$37.44	$37.45	$37.40
Purchase #3	$40.88	7.227%	$43.8344	$43.83	$43.85	$43.80
Purchase #4	$166.72	12.420%	$187.4266	$187.43	$187.45	$187.40
Purchase #5	$214.56	7.314%	$230.2529	$230.25	$230.25	$230.30
Purchase #6	$149.64	10.219%	$164.9317	$164.93	$164.95	$164.90
Purchase #7	$13.80	10.562%	$15.2576	$15.26	$15.25	$15.30
7 purchase totals =	$757.70		$827.3633	$827.36	$827.40	$827.30