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	$81.46	11.649%	$90.9493	$90.95	$90.95	$90.90
Purchase #2	$85.37	8.363%	$92.5095	$92.51	$92.50	$92.50
Purchase #3	$219.33	6.726%	$234.0821	$234.08	$234.10	$234.10
Purchase #4	$53.90	8.461%	$58.4605	$58.46	$58.45	$58.50
Purchase #5	$31.49	4.195%	$32.811	$32.81	$32.80	$32.80
Purchase #6	$226.32	13.444%	$256.7465	$256.75	$256.75	$256.70
Purchase #7	$65.69	11.280%	$73.0998	$73.10	$73.10	$73.10
7 purchase totals =	$763.56		$838.6587	$838.66	$838.65	$838.60