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	$245.28	5.822%	$259.5602	$259.56	$259.55	$259.60
Purchase #2	$62.62	7.488%	$67.309	$67.31	$67.30	$67.30
Purchase #3	$34.73	11.338%	$38.6677	$38.67	$38.65	$38.70
Purchase #4	$81.68	4.372%	$85.251	$85.25	$85.25	$85.30
Purchase #5	$76.30	8.604%	$82.8649	$82.86	$82.85	$82.90
Purchase #6	$9.30	9.745%	$10.2063	$10.21	$10.20	$10.20
Purchase #7	$99.40	5.699%	$105.0648	$105.06	$105.05	$105.10
7 purchase totals =	$609.31		$648.9239	$648.92	$648.85	$649.10