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	$22.58	7.108%	$24.185	$24.19	$24.20	$24.20
Purchase #2	$138.91	4.382%	$144.997	$145.00	$145.00	$145.00
Purchase #3	$37.42	9.166%	$40.8499	$40.85	$40.85	$40.80
Purchase #4	$131.54	13.153%	$148.8415	$148.84	$148.85	$148.80
Purchase #5	$147.28	11.360%	$164.011	$164.01	$164.00	$164.00
Purchase #6	$186.45	5.420%	$196.5556	$196.56	$196.55	$196.60
Purchase #7	$173.45	9.657%	$190.2001	$190.20	$190.20	$190.20
7 purchase totals =	$837.63		$909.6401	$909.65	$909.65	$909.60