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	$155.45	8.703%	$168.9788	$168.98	$169.00	$169.00
Purchase #2	$55.38	10.573%	$61.2353	$61.24	$61.25	$61.20
Purchase #3	$184.38	3.415%	$190.6766	$190.68	$190.70	$190.70
Purchase #4	$121.83	7.202%	$130.6042	$130.60	$130.60	$130.60
Purchase #5	$100.80	13.498%	$114.406	$114.41	$114.40	$114.40
Purchase #6	$38.54	10.137%	$42.4468	$42.45	$42.45	$42.40
Purchase #7	$152.73	6.390%	$162.4894	$162.49	$162.50	$162.50
7 purchase totals =	$809.11		$870.8371	$870.85	$870.90	$870.80