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	$63.25	13.691%	$71.9096	$71.91	$71.90	$71.90
Purchase #2	$162.61	7.639%	$175.0318	$175.03	$175.05	$175.00
Purchase #3	$222.87	13.753%	$253.5213	$253.52	$253.50	$253.50
Purchase #4	$171.91	4.743%	$180.0637	$180.06	$180.05	$180.10
Purchase #5	$164.98	4.385%	$172.2144	$172.21	$172.20	$172.20
Purchase #6	$86.96	4.390%	$90.7775	$90.78	$90.80	$90.80
Purchase #7	$41.71	10.857%	$46.2385	$46.24	$46.25	$46.20
7 purchase totals =	$914.29		$989.7568	$989.75	$989.75	$989.70