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	$150.47	4.108%	$156.6513	$156.65	$156.65	$156.70
Purchase #2	$57.59	13.710%	$65.4856	$65.49	$65.50	$65.50
Purchase #3	$123.89	7.685%	$133.4109	$133.41	$133.40	$133.40
Purchase #4	$138.89	4.627%	$145.3164	$145.32	$145.30	$145.30
Purchase #5	$64.77	12.784%	$73.0502	$73.05	$73.05	$73.10
Purchase #6	$21.89	6.353%	$23.2807	$23.28	$23.30	$23.30
Purchase #7	$32.71	7.376%	$35.1227	$35.12	$35.10	$35.10
7 purchase totals =	$590.21		$632.3178	$632.32	$632.30	$632.40