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	$80.44	4.122%	$83.7557	$83.76	$83.75	$83.80
Purchase #2	$42.73	6.724%	$45.6032	$45.60	$45.60	$45.60
Purchase #3	$81.79	3.234%	$84.4351	$84.44	$84.45	$84.40
Purchase #4	$35.83	6.837%	$38.2797	$38.28	$38.30	$38.30
Purchase #5	$31.55	11.786%	$35.2685	$35.27	$35.25	$35.30
Purchase #6	$109.79	9.228%	$119.9214	$119.92	$119.90	$119.90
Purchase #7	$166.44	3.603%	$172.4368	$172.44	$172.45	$172.40
7 purchase totals =	$548.57		$579.7004	$579.71	$579.70	$579.70