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	$139.55	8.850%	$151.9002	$151.90	$151.90	$151.90
Purchase #2	$162.29	5.281%	$170.8605	$170.86	$170.85	$170.90
Purchase #3	$28.28	9.755%	$31.0387	$31.04	$31.05	$31.00
Purchase #4	$215.32	12.688%	$242.6398	$242.64	$242.65	$242.60
Purchase #5	$85.90	3.679%	$89.0603	$89.06	$89.05	$89.10
Purchase #6	$214.29	11.738%	$239.4434	$239.44	$239.45	$239.40
Purchase #7	$152.66	3.776%	$158.4244	$158.42	$158.40	$158.40
7 purchase totals =	$998.29		$1,083.3673	$1,083.36	$1,083.35	$1,083.30