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	$81.59	9.532%	$89.3672	$89.37	$89.35	$89.40
Purchase #2	$82.25	10.212%	$90.6494	$90.65	$90.65	$90.60
Purchase #3	$160.57	3.397%	$166.0246	$166.02	$166.00	$166.00
Purchase #4	$223.83	11.513%	$249.5995	$249.60	$249.60	$249.60
Purchase #5	$25.25	9.147%	$27.5596	$27.56	$27.55	$27.60
Purchase #6	$112.79	4.319%	$117.6614	$117.66	$117.65	$117.70
Purchase #7	$62.46	10.753%	$69.1763	$69.18	$69.20	$69.20
7 purchase totals =	$748.74		$810.0380	$810.04	$810.00	$810.10