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	$91.53	7.687%	$98.5659	$98.57	$98.55	$98.60
Purchase #2	$156.90	8.867%	$170.8123	$170.81	$170.80	$170.80
Purchase #3	$18.85	12.338%	$21.1757	$21.18	$21.20	$21.20
Purchase #4	$204.39	9.534%	$223.8765	$223.88	$223.90	$223.90
Purchase #5	$155.89	11.603%	$173.9779	$173.98	$174.00	$174.00
Purchase #6	$33.74	10.788%	$37.3799	$37.38	$37.40	$37.40
Purchase #7	$107.53	5.305%	$113.2345	$113.23	$113.25	$113.20
7 purchase totals =	$768.83		$839.0227	$839.03	$839.10	$839.10