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	$75.75	3.721%	$78.5687	$78.57	$78.55	$78.60
Purchase #2	$55.64	10.366%	$61.4076	$61.41	$61.40	$61.40
Purchase #3	$56.33	8.326%	$61.02	$61.02	$61.00	$61.00
Purchase #4	$90.92	13.664%	$103.3433	$103.34	$103.35	$103.30
Purchase #5	$61.25	10.622%	$67.756	$67.76	$67.75	$67.80
Purchase #6	$28.55	10.141%	$31.4453	$31.45	$31.45	$31.40
Purchase #7	$135.55	4.651%	$141.8544	$141.85	$141.85	$141.90
7 purchase totals =	$503.99		$545.3953	$545.40	$545.35	$545.40