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	$170.43	12.855%	$192.3388	$192.34	$192.35	$192.30
Purchase #2	$224.30	11.671%	$250.4781	$250.48	$250.50	$250.50
Purchase #3	$141.56	10.702%	$156.7098	$156.71	$156.70	$156.70
Purchase #4	$89.29	7.871%	$96.318	$96.32	$96.30	$96.30
Purchase #5	$108.50	13.699%	$123.3634	$123.36	$123.35	$123.40
Purchase #6	$235.77	8.484%	$255.7727	$255.77	$255.75	$255.80
Purchase #7	$30.98	12.420%	$34.8277	$34.83	$34.85	$34.80
7 purchase totals =	$1,000.83		$1,109.8085	$1,109.81	$1,109.80	$1,109.80