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	$29.79	4.316%	$31.0757	$31.08	$31.10	$31.10
Purchase #2	$244.38	4.526%	$255.4406	$255.44	$255.45	$255.40
Purchase #3	$67.94	8.693%	$73.846	$73.85	$73.85	$73.80
Purchase #4	$232.32	13.874%	$264.5521	$264.55	$264.55	$264.60
Purchase #5	$141.40	8.605%	$153.5675	$153.57	$153.55	$153.60
Purchase #6	$98.38	8.707%	$106.9459	$106.95	$106.95	$106.90
Purchase #7	$85.56	8.183%	$92.5614	$92.56	$92.55	$92.60
7 purchase totals =	$899.77		$977.9892	$978.00	$978.00	$978.00