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	$139.71	9.150%	$152.4935	$152.49	$152.50	$152.50
Purchase #2	$81.59	10.328%	$90.0166	$90.02	$90.00	$90.00
Purchase #3	$215.33	11.293%	$239.6472	$239.65	$239.65	$239.60
Purchase #4	$35.61	7.590%	$38.3128	$38.31	$38.30	$38.30
Purchase #5	$239.39	11.599%	$267.1568	$267.16	$267.15	$267.20
Purchase #6	$54.70	10.792%	$60.6032	$60.60	$60.60	$60.60
Purchase #7	$78.38	3.607%	$81.2072	$81.21	$81.20	$81.20
7 purchase totals =	$844.71		$929.4373	$929.44	$929.40	$929.40