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	$155.59	11.582%	$173.6104	$173.61	$173.60	$173.60
Purchase #2	$205.84	6.577%	$219.3781	$219.38	$219.40	$219.40
Purchase #3	$52.87	3.315%	$54.6226	$54.62	$54.60	$54.60
Purchase #4	$108.74	4.391%	$113.5148	$113.51	$113.50	$113.50
Purchase #5	$228.40	8.346%	$247.4623	$247.46	$247.45	$247.50
Purchase #6	$219.44	3.597%	$227.3333	$227.33	$227.35	$227.30
Purchase #7	$99.72	12.364%	$112.0494	$112.05	$112.05	$112.00
7 purchase totals =	$1,070.60		$1,147.9709	$1,147.96	$1,147.95	$1,147.90