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	$178.27	5.125%	$187.4063	$187.41	$187.40	$187.40
Purchase #2	$78.60	8.725%	$85.4579	$85.46	$85.45	$85.50
Purchase #3	$120.88	5.610%	$127.6614	$127.66	$127.65	$127.70
Purchase #4	$149.85	12.497%	$168.5768	$168.58	$168.60	$168.60
Purchase #5	$144.59	8.221%	$156.4767	$156.48	$156.50	$156.50
Purchase #6	$97.76	10.278%	$107.8078	$107.81	$107.80	$107.80
Purchase #7	$242.39	5.457%	$255.6172	$255.62	$255.60	$255.60
7 purchase totals =	$1,012.34		$1,089.0041	$1,089.02	$1,089.00	$1,089.10