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	$70.95	9.805%	$77.9066	$77.91	$77.90	$77.90
Purchase #2	$66.53	9.512%	$72.8583	$72.86	$72.85	$72.90
Purchase #3	$172.33	3.304%	$178.0238	$178.02	$178.00	$178.00
Purchase #4	$11.57	10.503%	$12.7852	$12.79	$12.80	$12.80
Purchase #5	$80.77	6.795%	$86.2583	$86.26	$86.25	$86.30
Purchase #6	$70.30	13.619%	$79.8742	$79.87	$79.85	$79.90
Purchase #7	$132.69	5.833%	$140.4298	$140.43	$140.45	$140.40
7 purchase totals =	$605.14		$648.1362	$648.14	$648.10	$648.20