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	$129.91	5.344%	$136.8524	$136.85	$136.85	$136.90
Purchase #2	$75.90	10.202%	$83.6433	$83.64	$83.65	$83.60
Purchase #3	$60.42	7.786%	$65.1243	$65.12	$65.10	$65.10
Purchase #4	$101.63	11.131%	$112.9424	$112.94	$112.95	$112.90
Purchase #5	$151.41	9.651%	$166.0226	$166.02	$166.00	$166.00
Purchase #6	$127.90	13.683%	$145.4006	$145.40	$145.40	$145.40
Purchase #7	$209.37	9.310%	$228.8623	$228.86	$228.85	$228.90
7 purchase totals =	$856.54		$938.8479	$938.83	$938.80	$938.80