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	$99.33	13.390%	$112.6303	$112.63	$112.65	$112.60
Purchase #2	$92.98	13.447%	$105.483	$105.48	$105.50	$105.50
Purchase #3	$129.88	8.548%	$140.9821	$140.98	$141.00	$141.00
Purchase #4	$191.86	12.543%	$215.925	$215.93	$215.95	$215.90
Purchase #5	$52.50	13.120%	$59.388	$59.39	$59.40	$59.40
Purchase #6	$23.77	6.107%	$25.2216	$25.22	$25.20	$25.20
Purchase #7	$149.71	5.853%	$158.4725	$158.47	$158.45	$158.50
7 purchase totals =	$740.03		$818.1025	$818.10	$818.15	$818.10