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	$225.58	8.774%	$245.3724	$245.37	$245.35	$245.40
Purchase #2	$246.27	13.481%	$279.4697	$279.47	$279.45	$279.50
Purchase #3	$186.56	7.513%	$200.5763	$200.58	$200.60	$200.60
Purchase #4	$22.93	11.646%	$25.6004	$25.60	$25.60	$25.60
Purchase #5	$19.83	7.360%	$21.2895	$21.29	$21.30	$21.30
Purchase #6	$141.54	7.423%	$152.0465	$152.05	$152.05	$152.00
Purchase #7	$50.69	10.122%	$55.8208	$55.82	$55.80	$55.80
7 purchase totals =	$893.40		$980.1756	$980.18	$980.15	$980.20