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	$28.43	3.796%	$29.5092	$29.51	$29.50	$29.50
Purchase #2	$119.95	6.458%	$127.6964	$127.70	$127.70	$127.70
Purchase #3	$102.48	8.551%	$111.2431	$111.24	$111.25	$111.20
Purchase #4	$179.86	13.706%	$204.5116	$204.51	$204.50	$204.50
Purchase #5	$42.32	4.799%	$44.3509	$44.35	$44.35	$44.40
Purchase #6	$173.68	13.730%	$197.5263	$197.53	$197.55	$197.50
Purchase #7	$78.91	6.328%	$83.9034	$83.90	$83.90	$83.90
7 purchase totals =	$725.63		$798.7409	$798.74	$798.75	$798.70