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	$54.39	11.422%	$60.6024	$60.60	$60.60	$60.60
Purchase #2	$57.50	3.396%	$59.4527	$59.45	$59.45	$59.50
Purchase #3	$67.94	13.242%	$76.9366	$76.94	$76.95	$76.90
Purchase #4	$36.68	9.469%	$40.1532	$40.15	$40.15	$40.20
Purchase #5	$209.49	8.435%	$227.1605	$227.16	$227.15	$227.20
Purchase #6	$166.80	8.733%	$181.3666	$181.37	$181.35	$181.40
Purchase #7	$169.90	8.511%	$184.3602	$184.36	$184.35	$184.40
7 purchase totals =	$762.70		$830.0322	$830.03	$830.00	$830.20