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	$97.65	11.701%	$109.076	$109.08	$109.10	$109.10
Purchase #2	$81.34	4.870%	$85.3013	$85.30	$85.30	$85.30
Purchase #3	$137.26	3.200%	$141.6523	$141.65	$141.65	$141.70
Purchase #4	$144.87	3.834%	$150.4243	$150.42	$150.40	$150.40
Purchase #5	$47.27	3.244%	$48.8034	$48.80	$48.80	$48.80
Purchase #6	$51.55	5.191%	$54.226	$54.23	$54.25	$54.20
Purchase #7	$81.44	11.416%	$90.7372	$90.74	$90.75	$90.70
7 purchase totals =	$641.38		$680.2205	$680.22	$680.25	$680.20