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	$152.56	9.703%	$167.3629	$167.36	$167.35	$167.40
Purchase #2	$153.29	8.785%	$166.7565	$166.76	$166.75	$166.80
Purchase #3	$139.75	4.164%	$145.5692	$145.57	$145.55	$145.60
Purchase #4	$92.36	11.868%	$103.3213	$103.32	$103.30	$103.30
Purchase #5	$165.75	7.348%	$177.9293	$177.93	$177.95	$177.90
Purchase #6	$53.88	10.847%	$59.7244	$59.72	$59.70	$59.70
Purchase #7	$89.56	12.693%	$100.9279	$100.93	$100.95	$100.90
7 purchase totals =	$847.15		$921.5915	$921.59	$921.55	$921.60