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	$48.76	11.466%	$54.3508	$54.35	$54.35	$54.40
Purchase #2	$182.70	10.339%	$201.5894	$201.59	$201.60	$201.60
Purchase #3	$171.81	5.195%	$180.7355	$180.74	$180.75	$180.70
Purchase #4	$56.82	4.618%	$59.4439	$59.44	$59.45	$59.40
Purchase #5	$127.58	9.271%	$139.4079	$139.41	$139.40	$139.40
Purchase #6	$125.32	6.253%	$133.1563	$133.16	$133.15	$133.20
Purchase #7	$240.35	9.378%	$262.89	$262.89	$262.90	$262.90
7 purchase totals =	$953.34		$1,031.5738	$1,031.58	$1,031.60	$1,031.60