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	$91.27	12.872%	$103.0183	$103.02	$103.00	$103.00
Purchase #2	$219.92	10.846%	$243.7725	$243.77	$243.75	$243.80
Purchase #3	$225.82	3.574%	$233.8908	$233.89	$233.90	$233.90
Purchase #4	$37.67	13.833%	$42.8809	$42.88	$42.90	$42.90
Purchase #5	$24.98	11.464%	$27.8437	$27.84	$27.85	$27.80
Purchase #6	$18.72	5.505%	$19.7505	$19.75	$19.75	$19.80
Purchase #7	$99.90	12.163%	$112.0508	$112.05	$112.05	$112.10
7 purchase totals =	$718.28		$783.2075	$783.20	$783.20	$783.30