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	$199.69	5.299%	$210.2716	$210.27	$210.25	$210.30
Purchase #2	$106.28	9.286%	$116.1492	$116.15	$116.15	$116.10
Purchase #3	$80.47	11.136%	$89.4311	$89.43	$89.45	$89.40
Purchase #4	$48.38	11.166%	$53.7821	$53.78	$53.80	$53.80
Purchase #5	$142.30	13.177%	$161.0509	$161.05	$161.05	$161.10
Purchase #6	$106.91	10.468%	$118.1013	$118.10	$118.10	$118.10
Purchase #7	$225.25	10.860%	$249.7122	$249.71	$249.70	$249.70
7 purchase totals =	$909.28		$998.4984	$998.49	$998.50	$998.50