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	$136.64	6.346%	$145.3112	$145.31	$145.30	$145.30
Purchase #2	$173.57	3.122%	$178.9889	$178.99	$179.00	$179.00
Purchase #3	$130.53	8.329%	$141.4018	$141.40	$141.40	$141.40
Purchase #4	$49.56	11.856%	$55.4358	$55.44	$55.45	$55.40
Purchase #5	$177.89	12.519%	$200.16	$200.16	$200.15	$200.20
Purchase #6	$86.85	6.528%	$92.5196	$92.52	$92.50	$92.50
Purchase #7	$162.48	10.464%	$179.4819	$179.48	$179.50	$179.50
7 purchase totals =	$917.52		$993.2992	$993.30	$993.30	$993.30