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	$141.69	4.602%	$148.2106	$148.21	$148.20	$148.20
Purchase #2	$241.42	12.208%	$270.8926	$270.89	$270.90	$270.90
Purchase #3	$163.37	12.867%	$184.3908	$184.39	$184.40	$184.40
Purchase #4	$89.69	12.424%	$100.8331	$100.83	$100.85	$100.80
Purchase #5	$246.55	10.452%	$272.3194	$272.32	$272.30	$272.30
Purchase #6	$63.28	11.287%	$70.4224	$70.42	$70.40	$70.40
Purchase #7	$145.95	5.291%	$153.6722	$153.67	$153.65	$153.70
7 purchase totals =	$1,091.95		$1,200.7411	$1,200.73	$1,200.70	$1,200.70