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	$230.45	12.785%	$259.913	$259.91	$259.90	$259.90
Purchase #2	$47.90	13.745%	$54.4839	$54.48	$54.50	$54.50
Purchase #3	$19.66	11.147%	$21.8515	$21.85	$21.85	$21.90
Purchase #4	$158.60	5.474%	$167.2818	$167.28	$167.30	$167.30
Purchase #5	$189.33	8.666%	$205.7373	$205.74	$205.75	$205.70
Purchase #6	$99.67	12.229%	$111.8586	$111.86	$111.85	$111.90
Purchase #7	$144.57	12.512%	$162.6586	$162.66	$162.65	$162.70
7 purchase totals =	$890.18		$983.7847	$983.78	$983.80	$983.90