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	$174.77	8.684%	$189.947	$189.95	$189.95	$189.90
Purchase #2	$24.82	10.320%	$27.3814	$27.38	$27.40	$27.40
Purchase #3	$80.95	6.700%	$86.3737	$86.37	$86.35	$86.40
Purchase #4	$42.66	8.556%	$46.31	$46.31	$46.30	$46.30
Purchase #5	$177.27	8.793%	$192.8574	$192.86	$192.85	$192.90
Purchase #6	$30.52	7.637%	$32.8508	$32.85	$32.85	$32.90
Purchase #7	$12.83	3.798%	$13.3173	$13.32	$13.30	$13.30
7 purchase totals =	$543.82		$589.0376	$589.04	$589.00	$589.10