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	4.495%	$85.1216	$85.12	$85.10	$85.10
Purchase #2	$106.74	6.485%	$113.6621	$113.66	$113.65	$113.70
Purchase #3	$152.80	10.336%	$168.5934	$168.59	$168.60	$168.60
Purchase #4	$9.92	6.629%	$10.5776	$10.58	$10.60	$10.60
Purchase #5	$175.92	5.439%	$185.4883	$185.49	$185.50	$185.50
Purchase #6	$227.78	12.302%	$255.8015	$255.80	$255.80	$255.80
Purchase #7	$9.41	11.611%	$10.5026	$10.50	$10.50	$10.50
7 purchase totals =	$764.03		$829.7471	$829.74	$829.75	$829.80