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	$18.46	9.255%	$20.1685	$20.17	$20.15	$20.20
Purchase #2	$63.57	11.462%	$70.8564	$70.86	$70.85	$70.90
Purchase #3	$92.56	6.814%	$98.867	$98.87	$98.85	$98.90
Purchase #4	$151.50	5.648%	$160.0567	$160.06	$160.05	$160.10
Purchase #5	$241.92	9.113%	$263.9662	$263.97	$263.95	$264.00
Purchase #6	$12.54	8.335%	$13.5852	$13.59	$13.60	$13.60
Purchase #7	$212.25	12.407%	$238.5839	$238.58	$238.60	$238.60
7 purchase totals =	$792.80		$866.0839	$866.10	$866.05	$866.30