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	$71.57	8.571%	$77.7043	$77.70	$77.70	$77.70
Purchase #2	$81.27	11.467%	$90.5892	$90.59	$90.60	$90.60
Purchase #3	$169.50	4.352%	$176.8766	$176.88	$176.90	$176.90
Purchase #4	$95.76	12.218%	$107.46	$107.46	$107.45	$107.50
Purchase #5	$196.71	5.796%	$208.1113	$208.11	$208.10	$208.10
Purchase #6	$11.33	9.836%	$12.4444	$12.44	$12.45	$12.40
Purchase #7	$84.25	3.194%	$86.9409	$86.94	$86.95	$86.90
7 purchase totals =	$710.39		$760.1267	$760.12	$760.15	$760.10