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	$7.76	12.862%	$8.7581	$8.76	$8.75	$8.80
Purchase #2	$100.32	12.525%	$112.8851	$112.89	$112.90	$112.90
Purchase #3	$238.41	5.180%	$250.7596	$250.76	$250.75	$250.80
Purchase #4	$158.81	9.400%	$173.7381	$173.74	$173.75	$173.70
Purchase #5	$90.59	8.789%	$98.552	$98.55	$98.55	$98.60
Purchase #6	$107.32	4.336%	$111.9734	$111.97	$111.95	$112.00
Purchase #7	$56.87	8.287%	$61.5828	$61.58	$61.60	$61.60
7 purchase totals =	$760.08		$818.2491	$818.25	$818.25	$818.40