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	$245.31	13.379%	$278.13	$278.13	$278.15	$278.10
Purchase #2	$228.90	4.349%	$238.8549	$238.85	$238.85	$238.90
Purchase #3	$35.70	5.224%	$37.565	$37.57	$37.55	$37.60
Purchase #4	$145.96	11.275%	$162.417	$162.42	$162.40	$162.40
Purchase #5	$64.58	9.125%	$70.4729	$70.47	$70.45	$70.50
Purchase #6	$41.40	13.386%	$46.9418	$46.94	$46.95	$46.90
Purchase #7	$54.31	9.532%	$59.4868	$59.49	$59.50	$59.50
7 purchase totals =	$816.16		$893.8684	$893.87	$893.85	$893.90