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	$245.90	9.353%	$268.899	$268.90	$268.90	$268.90
Purchase #2	$47.39	5.553%	$50.0216	$50.02	$50.00	$50.00
Purchase #3	$230.56	10.734%	$255.3083	$255.31	$255.30	$255.30
Purchase #4	$64.77	12.317%	$72.7477	$72.75	$72.75	$72.70
Purchase #5	$29.90	6.787%	$31.9293	$31.93	$31.95	$31.90
Purchase #6	$37.33	10.752%	$41.3437	$41.34	$41.35	$41.30
Purchase #7	$158.42	5.500%	$167.1331	$167.13	$167.15	$167.10
7 purchase totals =	$814.27		$887.3827	$887.38	$887.40	$887.20