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	$42.80	11.791%	$47.8465	$47.85	$47.85	$47.80
Purchase #2	$133.80	8.158%	$144.7154	$144.72	$144.70	$144.70
Purchase #3	$128.41	3.108%	$132.401	$132.40	$132.40	$132.40
Purchase #4	$141.60	7.747%	$152.5698	$152.57	$152.55	$152.60
Purchase #5	$132.52	6.585%	$141.2464	$141.25	$141.25	$141.20
Purchase #6	$149.83	13.422%	$169.9402	$169.94	$169.95	$169.90
Purchase #7	$250.93	11.229%	$279.1069	$279.11	$279.10	$279.10
7 purchase totals =	$979.89		$1,067.8262	$1,067.84	$1,067.80	$1,067.70