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	$111.53	8.415%	$120.9152	$120.92	$120.90	$120.90
Purchase #2	$34.53	10.365%	$38.109	$38.11	$38.10	$38.10
Purchase #3	$186.83	5.188%	$196.5227	$196.52	$196.50	$196.50
Purchase #4	$64.54	7.107%	$69.1269	$69.13	$69.15	$69.10
Purchase #5	$164.77	10.143%	$181.4826	$181.48	$181.50	$181.50
Purchase #6	$130.98	10.125%	$144.2417	$144.24	$144.25	$144.20
Purchase #7	$91.84	12.291%	$103.1281	$103.13	$103.15	$103.10
7 purchase totals =	$785.02		$853.5262	$853.53	$853.55	$853.40