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	$188.33	6.509%	$200.5884	$200.59	$200.60	$200.60
Purchase #2	$29.46	11.572%	$32.8691	$32.87	$32.85	$32.90
Purchase #3	$47.88	5.811%	$50.6623	$50.66	$50.65	$50.70
Purchase #4	$158.27	13.563%	$179.7362	$179.74	$179.75	$179.70
Purchase #5	$201.57	7.566%	$216.8208	$216.82	$216.80	$216.80
Purchase #6	$61.46	9.874%	$67.5286	$67.53	$67.55	$67.50
Purchase #7	$98.40	13.249%	$111.437	$111.44	$111.45	$111.40
7 purchase totals =	$785.37		$859.6424	$859.65	$859.65	$859.60