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	$150.31	6.391%	$159.9163	$159.92	$159.90	$159.90
Purchase #2	$213.85	13.254%	$242.1937	$242.19	$242.20	$242.20
Purchase #3	$164.27	5.379%	$173.1061	$173.11	$173.10	$173.10
Purchase #4	$56.72	10.151%	$62.4776	$62.48	$62.50	$62.50
Purchase #5	$122.78	13.326%	$139.1417	$139.14	$139.15	$139.10
Purchase #6	$72.86	6.180%	$77.3627	$77.36	$77.35	$77.40
Purchase #7	$14.88	6.826%	$15.8957	$15.90	$15.90	$15.90
7 purchase totals =	$795.67		$870.0938	$870.10	$870.10	$870.10