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	$25.81	7.689%	$27.7945	$27.79	$27.80	$27.80
Purchase #2	$128.26	3.346%	$132.5516	$132.55	$132.55	$132.60
Purchase #3	$50.58	4.669%	$52.9416	$52.94	$52.95	$52.90
Purchase #4	$7.54	13.846%	$8.584	$8.58	$8.60	$8.60
Purchase #5	$85.65	7.417%	$92.0027	$92.00	$92.00	$92.00
Purchase #6	$44.33	3.382%	$45.8292	$45.83	$45.85	$45.80
Purchase #7	$54.59	5.169%	$57.4118	$57.41	$57.40	$57.40
7 purchase totals =	$396.76		$417.1154	$417.10	$417.15	$417.10