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	$234.64	12.444%	$263.8386	$263.84	$263.85	$263.80
Purchase #2	$167.96	12.700%	$189.2909	$189.29	$189.30	$189.30
Purchase #3	$41.31	12.311%	$46.3957	$46.40	$46.40	$46.40
Purchase #4	$158.66	7.323%	$170.2787	$170.28	$170.30	$170.30
Purchase #5	$49.25	5.862%	$52.137	$52.14	$52.15	$52.10
Purchase #6	$85.85	5.461%	$90.5383	$90.54	$90.55	$90.50
Purchase #7	$41.91	3.372%	$43.3232	$43.32	$43.30	$43.30
7 purchase totals =	$779.58		$855.8024	$855.81	$855.85	$855.70