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	$6.30	11.122%	$7.0007	$7.00	$7.00	$7.00
Purchase #2	$43.68	12.361%	$49.0793	$49.08	$49.10	$49.10
Purchase #3	$43.35	9.557%	$47.493	$47.49	$47.50	$47.50
Purchase #4	$141.33	12.460%	$158.9397	$158.94	$158.95	$158.90
Purchase #5	$219.73	13.622%	$249.6616	$249.66	$249.65	$249.70
Purchase #6	$37.31	9.377%	$40.8086	$40.81	$40.80	$40.80
Purchase #7	$162.60	5.476%	$171.504	$171.50	$171.50	$171.50
7 purchase totals =	$654.30		$724.4869	$724.48	$724.50	$724.50