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	$19.92	6.746%	$21.2638	$21.26	$21.25	$21.30
Purchase #2	$195.56	10.648%	$216.3832	$216.38	$216.40	$216.40
Purchase #3	$79.39	8.338%	$86.0095	$86.01	$86.00	$86.00
Purchase #4	$10.25	6.301%	$10.8959	$10.90	$10.90	$10.90
Purchase #5	$130.43	13.539%	$148.0889	$148.09	$148.10	$148.10
Purchase #6	$66.25	7.817%	$71.4288	$71.43	$71.45	$71.40
Purchase #7	$102.59	10.743%	$113.6112	$113.61	$113.60	$113.60
7 purchase totals =	$604.39		$667.6813	$667.68	$667.70	$667.70