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	$25.48	6.803%	$27.2134	$27.21	$27.20	$27.20
Purchase #2	$51.41	7.500%	$55.2658	$55.27	$55.25	$55.30
Purchase #3	$16.57	9.575%	$18.1566	$18.16	$18.15	$18.20
Purchase #4	$238.77	8.118%	$258.1533	$258.15	$258.15	$258.20
Purchase #5	$196.71	13.153%	$222.5833	$222.58	$222.60	$222.60
Purchase #6	$72.36	11.456%	$80.6496	$80.65	$80.65	$80.60
Purchase #7	$74.64	6.524%	$79.5095	$79.51	$79.50	$79.50
7 purchase totals =	$675.94		$741.5315	$741.53	$741.50	$741.60