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	$250.27	5.805%	$264.7982	$264.80	$264.80	$264.80
Purchase #2	$159.85	3.141%	$164.8709	$164.87	$164.85	$164.90
Purchase #3	$14.27	3.733%	$14.8027	$14.80	$14.80	$14.80
Purchase #4	$180.55	6.498%	$192.2821	$192.28	$192.30	$192.30
Purchase #5	$158.47	13.470%	$179.8159	$179.82	$179.80	$179.80
Purchase #6	$56.48	13.684%	$64.2087	$64.21	$64.20	$64.20
Purchase #7	$80.29	4.411%	$83.8316	$83.83	$83.85	$83.80
7 purchase totals =	$900.18		$964.6101	$964.61	$964.60	$964.60