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	$39.32	8.571%	$42.6901	$42.69	$42.70	$42.70
Purchase #2	$241.49	10.365%	$266.5204	$266.52	$266.50	$266.50
Purchase #3	$229.78	3.592%	$238.0337	$238.03	$238.05	$238.00
Purchase #4	$70.76	4.430%	$73.8947	$73.89	$73.90	$73.90
Purchase #5	$85.77	4.373%	$89.5207	$89.52	$89.50	$89.50
Purchase #6	$98.62	8.211%	$106.7177	$106.72	$106.70	$106.70
Purchase #7	$155.55	10.716%	$172.2187	$172.22	$172.20	$172.20
7 purchase totals =	$921.29		$989.5960	$989.59	$989.55	$989.50