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	$59.51	11.647%	$66.4411	$66.44	$66.45	$66.40
Purchase #2	$57.59	3.552%	$59.6356	$59.64	$59.65	$59.60
Purchase #3	$215.58	8.614%	$234.1501	$234.15	$234.15	$234.20
Purchase #4	$249.45	10.772%	$276.3208	$276.32	$276.30	$276.30
Purchase #5	$30.49	8.584%	$33.1073	$33.11	$33.10	$33.10
Purchase #6	$168.58	4.123%	$175.5306	$175.53	$175.55	$175.50
Purchase #7	$64.33	9.810%	$70.6408	$70.64	$70.65	$70.60
7 purchase totals =	$845.53		$915.8263	$915.83	$915.85	$915.70