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	$168.65	6.746%	$180.0271	$180.03	$180.05	$180.00
Purchase #2	$139.81	5.213%	$147.0983	$147.10	$147.10	$147.10
Purchase #3	$19.79	4.792%	$20.7383	$20.74	$20.75	$20.70
Purchase #4	$101.95	7.276%	$109.3679	$109.37	$109.35	$109.40
Purchase #5	$37.71	11.762%	$42.1455	$42.15	$42.15	$42.10
Purchase #6	$249.37	8.786%	$271.2796	$271.28	$271.30	$271.30
Purchase #7	$100.79	8.760%	$109.6192	$109.62	$109.60	$109.60
7 purchase totals =	$818.07		$880.2759	$880.29	$880.30	$880.20