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	$123.59	6.261%	$131.328	$131.33	$131.35	$131.30
Purchase #2	$60.27	9.160%	$65.7907	$65.79	$65.80	$65.80
Purchase #3	$89.86	9.777%	$98.6456	$98.65	$98.65	$98.60
Purchase #4	$56.70	4.788%	$59.4148	$59.41	$59.40	$59.40
Purchase #5	$34.52	11.488%	$38.4857	$38.49	$38.50	$38.50
Purchase #6	$49.89	12.753%	$56.2525	$56.25	$56.25	$56.30
Purchase #7	$210.28	11.671%	$234.8218	$234.82	$234.80	$234.80
7 purchase totals =	$625.11		$684.7391	$684.74	$684.75	$684.70