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	$20.99	10.745%	$23.2454	$23.25	$23.25	$23.20
Purchase #2	$146.47	13.147%	$165.7264	$165.73	$165.75	$165.70
Purchase #3	$73.62	7.216%	$78.9324	$78.93	$78.95	$78.90
Purchase #4	$220.91	6.131%	$234.454	$234.45	$234.45	$234.50
Purchase #5	$184.27	6.573%	$196.3821	$196.38	$196.40	$196.40
Purchase #6	$111.27	11.255%	$123.7934	$123.79	$123.80	$123.80
Purchase #7	$228.43	11.778%	$255.3345	$255.33	$255.35	$255.30
7 purchase totals =	$985.96		$1,077.8682	$1,077.86	$1,077.95	$1,077.80