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	$125.70	4.389%	$131.217	$131.22	$131.20	$131.20
Purchase #2	$188.87	13.590%	$214.5374	$214.54	$214.55	$214.50
Purchase #3	$222.85	12.334%	$250.3363	$250.34	$250.35	$250.30
Purchase #4	$194.27	10.444%	$214.5596	$214.56	$214.55	$214.60
Purchase #5	$29.45	11.854%	$32.941	$32.94	$32.95	$32.90
Purchase #6	$229.53	11.495%	$255.9145	$255.91	$255.90	$255.90
Purchase #7	$74.37	6.845%	$79.4606	$79.46	$79.45	$79.50
7 purchase totals =	$1,065.04		$1,178.9664	$1,178.97	$1,178.95	$1,178.90