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	$165.72	6.217%	$176.0228	$176.02	$176.00	$176.00
Purchase #2	$163.37	9.286%	$178.5405	$178.54	$178.55	$178.50
Purchase #3	$96.37	5.838%	$101.9961	$102.00	$102.00	$102.00
Purchase #4	$123.83	6.185%	$131.4889	$131.49	$131.50	$131.50
Purchase #5	$42.39	7.689%	$45.6494	$45.65	$45.65	$45.60
Purchase #6	$202.85	13.154%	$229.5329	$229.53	$229.55	$229.50
Purchase #7	$87.83	9.652%	$96.3074	$96.31	$96.30	$96.30
7 purchase totals =	$882.36		$959.5380	$959.54	$959.55	$959.40