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	$131.42	11.388%	$146.3861	$146.39	$146.40	$146.40
Purchase #2	$153.79	13.246%	$174.161	$174.16	$174.15	$174.20
Purchase #3	$114.32	7.728%	$123.1546	$123.15	$123.15	$123.20
Purchase #4	$128.54	3.538%	$133.0877	$133.09	$133.10	$133.10
Purchase #5	$148.73	9.441%	$162.7716	$162.77	$162.75	$162.80
Purchase #6	$32.54	9.325%	$35.5744	$35.57	$35.55	$35.60
Purchase #7	$63.81	8.776%	$69.41	$69.41	$69.40	$69.40
7 purchase totals =	$773.15		$844.5454	$844.54	$844.50	$844.70