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	$110.66	12.835%	$124.8632	$124.86	$124.85	$124.90
Purchase #2	$78.94	4.811%	$82.7378	$82.74	$82.75	$82.70
Purchase #3	$215.61	10.588%	$238.4388	$238.44	$238.45	$238.40
Purchase #4	$167.36	5.325%	$176.2719	$176.27	$176.25	$176.30
Purchase #5	$26.31	10.777%	$29.1454	$29.15	$29.15	$29.10
Purchase #6	$10.57	4.853%	$11.083	$11.08	$11.10	$11.10
Purchase #7	$127.31	11.141%	$141.4936	$141.49	$141.50	$141.50
7 purchase totals =	$736.76		$804.0337	$804.03	$804.05	$804.00