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	$32.38	10.851%	$35.8936	$35.89	$35.90	$35.90
Purchase #2	$12.96	11.448%	$14.4437	$14.44	$14.45	$14.40
Purchase #3	$209.39	12.468%	$235.4967	$235.50	$235.50	$235.50
Purchase #4	$151.48	10.107%	$166.7901	$166.79	$166.80	$166.80
Purchase #5	$35.97	12.541%	$40.481	$40.48	$40.50	$40.50
Purchase #6	$35.61	13.428%	$40.3917	$40.39	$40.40	$40.40
Purchase #7	$52.32	7.463%	$56.2246	$56.22	$56.20	$56.20
7 purchase totals =	$530.11		$589.7214	$589.71	$589.75	$589.70