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	$172.96	3.661%	$179.2921	$179.29	$179.30	$179.30
Purchase #2	$190.90	11.767%	$213.3632	$213.36	$213.35	$213.40
Purchase #3	$130.75	8.565%	$141.9487	$141.95	$141.95	$141.90
Purchase #4	$12.59	11.814%	$14.0774	$14.08	$14.10	$14.10
Purchase #5	$85.68	5.572%	$90.4541	$90.45	$90.45	$90.50
Purchase #6	$95.79	10.294%	$105.6506	$105.65	$105.65	$105.70
Purchase #7	$126.44	12.632%	$142.4119	$142.41	$142.40	$142.40
7 purchase totals =	$815.11		$887.1980	$887.19	$887.20	$887.30