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	$133.53	6.471%	$142.1707	$142.17	$142.15	$142.20
Purchase #2	$244.59	12.340%	$274.7724	$274.77	$274.75	$274.80
Purchase #3	$75.57	10.330%	$83.3764	$83.38	$83.40	$83.40
Purchase #4	$50.93	4.606%	$53.2758	$53.28	$53.30	$53.30
Purchase #5	$93.25	13.263%	$105.6177	$105.62	$105.60	$105.60
Purchase #6	$165.81	7.253%	$177.8362	$177.84	$177.85	$177.80
Purchase #7	$60.32	4.170%	$62.8353	$62.84	$62.85	$62.80
7 purchase totals =	$824.00		$899.8845	$899.90	$899.90	$899.90