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	$77.95	3.390%	$80.5925	$80.59	$80.60	$80.60
Purchase #2	$59.88	4.178%	$62.3818	$62.38	$62.40	$62.40
Purchase #3	$150.70	5.825%	$159.4783	$159.48	$159.50	$159.50
Purchase #4	$31.93	10.298%	$35.2182	$35.22	$35.20	$35.20
Purchase #5	$154.95	8.667%	$168.3795	$168.38	$168.40	$168.40
Purchase #6	$96.83	8.588%	$105.1458	$105.15	$105.15	$105.10
Purchase #7	$114.79	9.367%	$125.5424	$125.54	$125.55	$125.50
7 purchase totals =	$687.03		$736.7385	$736.74	$736.80	$736.70