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	$90.64	11.291%	$100.8742	$100.87	$100.85	$100.90
Purchase #2	$114.55	8.105%	$123.8343	$123.83	$123.85	$123.80
Purchase #3	$64.78	13.485%	$73.5156	$73.52	$73.50	$73.50
Purchase #4	$84.79	3.813%	$88.023	$88.02	$88.00	$88.00
Purchase #5	$56.68	5.719%	$59.9215	$59.92	$59.90	$59.90
Purchase #6	$147.38	9.478%	$161.3487	$161.35	$161.35	$161.30
Purchase #7	$152.78	11.104%	$169.7447	$169.74	$169.75	$169.70
7 purchase totals =	$711.60		$777.2620	$777.25	$777.20	$777.10