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	$113.56	12.187%	$127.3996	$127.40	$127.40	$127.40
Purchase #2	$242.69	5.819%	$256.8121	$256.81	$256.80	$256.80
Purchase #3	$45.88	7.740%	$49.4311	$49.43	$49.45	$49.40
Purchase #4	$233.75	9.103%	$255.0283	$255.03	$255.05	$255.00
Purchase #5	$105.54	11.273%	$117.4375	$117.44	$117.45	$117.40
Purchase #6	$80.58	9.368%	$88.1287	$88.13	$88.15	$88.10
Purchase #7	$88.34	9.345%	$96.5954	$96.60	$96.60	$96.60
7 purchase totals =	$910.34		$990.8327	$990.84	$990.90	$990.70