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	$132.76	3.442%	$137.3296	$137.33	$137.35	$137.30
Purchase #2	$127.88	7.839%	$137.9045	$137.90	$137.90	$137.90
Purchase #3	$76.39	13.658%	$86.8233	$86.82	$86.80	$86.80
Purchase #4	$37.27	6.863%	$39.8278	$39.83	$39.85	$39.80
Purchase #5	$113.64	7.700%	$122.3903	$122.39	$122.40	$122.40
Purchase #6	$157.52	5.488%	$166.1647	$166.16	$166.15	$166.20
Purchase #7	$24.87	13.477%	$28.2217	$28.22	$28.20	$28.20
7 purchase totals =	$670.33		$718.6619	$718.65	$718.65	$718.60