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	$100.87	3.283%	$104.1816	$104.18	$104.20	$104.20
Purchase #2	$130.29	9.528%	$142.704	$142.70	$142.70	$142.70
Purchase #3	$170.56	11.866%	$190.7986	$190.80	$190.80	$190.80
Purchase #4	$190.81	13.364%	$216.3098	$216.31	$216.30	$216.30
Purchase #5	$163.79	9.519%	$179.3812	$179.38	$179.40	$179.40
Purchase #6	$91.37	12.287%	$102.5966	$102.60	$102.60	$102.60
Purchase #7	$77.46	8.342%	$83.9217	$83.92	$83.90	$83.90
7 purchase totals =	$925.15		$1,019.8935	$1,019.89	$1,019.90	$1,019.90