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	$12.41	4.448%	$12.962	$12.96	$12.95	$13.00
Purchase #2	$81.42	6.264%	$86.5201	$86.52	$86.50	$86.50
Purchase #3	$153.47	7.144%	$164.4339	$164.43	$164.45	$164.40
Purchase #4	$90.82	10.596%	$100.4433	$100.44	$100.45	$100.40
Purchase #5	$179.31	5.331%	$188.869	$188.87	$188.85	$188.90
Purchase #6	$82.26	6.525%	$87.6275	$87.63	$87.65	$87.60
Purchase #7	$221.31	3.597%	$229.2705	$229.27	$229.25	$229.30
7 purchase totals =	$821.00		$870.1263	$870.12	$870.10	$870.10