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	$172.46	4.396%	$180.0413	$180.04	$180.05	$180.00
Purchase #2	$104.56	9.348%	$114.3343	$114.33	$114.35	$114.30
Purchase #3	$155.88	9.618%	$170.8725	$170.87	$170.85	$170.90
Purchase #4	$176.39	5.324%	$185.781	$185.78	$185.80	$185.80
Purchase #5	$27.70	5.171%	$29.1324	$29.13	$29.15	$29.10
Purchase #6	$35.62	5.374%	$37.5342	$37.53	$37.55	$37.50
Purchase #7	$109.99	4.419%	$114.8505	$114.85	$114.85	$114.90
7 purchase totals =	$782.60		$832.5462	$832.53	$832.60	$832.50