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	$37.66	3.777%	$39.0824	$39.08	$39.10	$39.10
Purchase #2	$93.49	5.267%	$98.4141	$98.41	$98.40	$98.40
Purchase #3	$62.55	10.337%	$69.0158	$69.02	$69.00	$69.00
Purchase #4	$59.61	9.851%	$65.4822	$65.48	$65.50	$65.50
Purchase #5	$122.77	3.800%	$127.4353	$127.44	$127.45	$127.40
Purchase #6	$31.49	6.463%	$33.5252	$33.53	$33.55	$33.50
Purchase #7	$39.39	12.636%	$44.3673	$44.37	$44.35	$44.40
7 purchase totals =	$446.96		$477.3223	$477.33	$477.35	$477.30