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	$172.70	3.659%	$179.0191	$179.02	$179.00	$179.00
Purchase #2	$70.67	3.640%	$73.2424	$73.24	$73.25	$73.20
Purchase #3	$140.92	6.859%	$150.5857	$150.59	$150.60	$150.60
Purchase #4	$157.35	4.395%	$164.2655	$164.27	$164.25	$164.30
Purchase #5	$103.56	4.341%	$108.0555	$108.06	$108.05	$108.10
Purchase #6	$27.33	7.851%	$29.4757	$29.48	$29.50	$29.50
Purchase #7	$136.37	3.523%	$141.1743	$141.17	$141.15	$141.20
7 purchase totals =	$808.90		$845.8182	$845.83	$845.80	$845.90