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	$47.59	3.433%	$49.2238	$49.22	$49.20	$49.20
Purchase #2	$103.45	12.434%	$116.313	$116.31	$116.30	$116.30
Purchase #3	$134.53	13.372%	$152.5194	$152.52	$152.50	$152.50
Purchase #4	$12.61	5.571%	$13.3125	$13.31	$13.30	$13.30
Purchase #5	$11.85	10.717%	$13.12	$13.12	$13.10	$13.10
Purchase #6	$210.54	13.111%	$238.1439	$238.14	$238.15	$238.10
Purchase #7	$79.38	13.270%	$89.9137	$89.91	$89.90	$89.90
7 purchase totals =	$599.95		$672.5463	$672.53	$672.45	$672.40