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	$86.57	4.540%	$90.5003	$90.50	$90.50	$90.50
Purchase #2	$115.66	12.722%	$130.3743	$130.37	$130.35	$130.40
Purchase #3	$86.69	13.600%	$98.4798	$98.48	$98.50	$98.50
Purchase #4	$215.28	10.305%	$237.4646	$237.46	$237.45	$237.50
Purchase #5	$74.95	13.781%	$85.2789	$85.28	$85.30	$85.30
Purchase #6	$173.97	13.200%	$196.934	$196.93	$196.95	$196.90
Purchase #7	$160.43	11.594%	$179.0303	$179.03	$179.05	$179.00
7 purchase totals =	$913.55		$1,018.0622	$1,018.05	$1,018.10	$1,018.10