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	$24.50	12.405%	$27.5392	$27.54	$27.55	$27.50
Purchase #2	$110.72	3.470%	$114.562	$114.56	$114.55	$114.60
Purchase #3	$58.37	11.748%	$65.2273	$65.23	$65.25	$65.20
Purchase #4	$52.49	4.270%	$54.7313	$54.73	$54.75	$54.70
Purchase #5	$151.40	10.245%	$166.9109	$166.91	$166.90	$166.90
Purchase #6	$130.47	12.126%	$146.2908	$146.29	$146.30	$146.30
Purchase #7	$85.45	11.268%	$95.0785	$95.08	$95.10	$95.10
7 purchase totals =	$613.40		$670.3400	$670.34	$670.40	$670.30