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	$78.79	12.338%	$88.5111	$88.51	$88.50	$88.50
Purchase #2	$156.42	12.763%	$176.3839	$176.38	$176.40	$176.40
Purchase #3	$62.84	13.110%	$71.0783	$71.08	$71.10	$71.10
Purchase #4	$48.86	3.545%	$50.5921	$50.59	$50.60	$50.60
Purchase #5	$164.67	10.142%	$181.3708	$181.37	$181.35	$181.40
Purchase #6	$72.41	12.707%	$81.6111	$81.61	$81.60	$81.60
Purchase #7	$182.55	3.414%	$188.7823	$188.78	$188.80	$188.80
7 purchase totals =	$766.54		$838.3296	$838.32	$838.35	$838.40