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	$104.49	10.604%	$115.5701	$115.57	$115.55	$115.60
Purchase #2	$29.53	9.821%	$32.4301	$32.43	$32.45	$32.40
Purchase #3	$82.71	8.552%	$89.7834	$89.78	$89.80	$89.80
Purchase #4	$218.40	9.537%	$239.2288	$239.23	$239.25	$239.20
Purchase #5	$31.98	11.439%	$35.6382	$35.64	$35.65	$35.60
Purchase #6	$79.43	4.333%	$82.8717	$82.87	$82.85	$82.90
Purchase #7	$88.69	12.390%	$99.6787	$99.68	$99.70	$99.70
7 purchase totals =	$635.23		$695.2010	$695.20	$695.25	$695.20