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	$73.47	10.330%	$81.0595	$81.06	$81.05	$81.10
Purchase #2	$86.33	4.456%	$90.1769	$90.18	$90.20	$90.20
Purchase #3	$234.60	12.270%	$263.3854	$263.39	$263.40	$263.40
Purchase #4	$181.83	4.742%	$190.4524	$190.45	$190.45	$190.50
Purchase #5	$37.79	11.573%	$42.1634	$42.16	$42.15	$42.20
Purchase #6	$35.61	6.375%	$37.8801	$37.88	$37.90	$37.90
Purchase #7	$14.40	10.194%	$15.8679	$15.87	$15.85	$15.90
7 purchase totals =	$664.03		$720.9856	$720.99	$721.00	$721.20