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	$104.28	6.700%	$111.2668	$111.27	$111.25	$111.30
Purchase #2	$204.87	12.168%	$229.7986	$229.80	$229.80	$229.80
Purchase #3	$150.26	9.534%	$164.5858	$164.59	$164.60	$164.60
Purchase #4	$84.67	13.711%	$96.2791	$96.28	$96.30	$96.30
Purchase #5	$202.45	8.814%	$220.2939	$220.29	$220.30	$220.30
Purchase #6	$51.37	8.301%	$55.6342	$55.63	$55.65	$55.60
Purchase #7	$156.46	6.630%	$166.8333	$166.83	$166.85	$166.80
7 purchase totals =	$954.36		$1,044.6917	$1,044.69	$1,044.75	$1,044.70