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	$231.96	5.367%	$244.4093	$244.41	$244.40	$244.40
Purchase #2	$100.86	8.446%	$109.3786	$109.38	$109.40	$109.40
Purchase #3	$223.61	3.665%	$231.8053	$231.81	$231.80	$231.80
Purchase #4	$32.31	5.747%	$34.1669	$34.17	$34.15	$34.20
Purchase #5	$236.84	3.582%	$245.3236	$245.32	$245.30	$245.30
Purchase #6	$78.60	13.316%	$89.0664	$89.07	$89.05	$89.10
Purchase #7	$147.54	4.235%	$153.7883	$153.79	$153.80	$153.80
7 purchase totals =	$1,051.72		$1,107.9384	$1,107.95	$1,107.90	$1,108.00