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	$144.54	11.661%	$161.3948	$161.39	$161.40	$161.40
Purchase #2	$70.53	12.864%	$79.603	$79.60	$79.60	$79.60
Purchase #3	$53.94	7.529%	$58.0011	$58.00	$58.00	$58.00
Purchase #4	$63.38	3.667%	$65.7041	$65.70	$65.70	$65.70
Purchase #5	$19.81	5.521%	$20.9037	$20.90	$20.90	$20.90
Purchase #6	$245.63	9.582%	$269.1663	$269.17	$269.15	$269.20
Purchase #7	$10.99	12.660%	$12.3813	$12.38	$12.40	$12.40
7 purchase totals =	$608.82		$667.1543	$667.14	$667.15	$667.20