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	$9.27	6.472%	$9.87	$9.87	$9.85	$9.90
Purchase #2	$162.39	4.348%	$169.4507	$169.45	$169.45	$169.50
Purchase #3	$158.27	6.614%	$168.738	$168.74	$168.75	$168.70
Purchase #4	$228.50	13.525%	$259.4046	$259.40	$259.40	$259.40
Purchase #5	$63.44	11.455%	$70.7071	$70.71	$70.70	$70.70
Purchase #6	$136.33	3.300%	$140.8289	$140.83	$140.85	$140.80
Purchase #7	$111.27	11.181%	$123.7111	$123.71	$123.70	$123.70
7 purchase totals =	$869.47		$942.7104	$942.71	$942.70	$942.70