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	$18.54	6.399%	$19.7264	$19.73	$19.75	$19.70
Purchase #2	$82.29	4.871%	$86.2983	$86.30	$86.30	$86.30
Purchase #3	$179.78	4.778%	$188.3699	$188.37	$188.35	$188.40
Purchase #4	$115.38	10.579%	$127.5861	$127.59	$127.60	$127.60
Purchase #5	$175.49	5.797%	$185.6632	$185.66	$185.65	$185.70
Purchase #6	$74.47	10.250%	$82.1032	$82.10	$82.10	$82.10
Purchase #7	$43.42	4.282%	$45.2792	$45.28	$45.30	$45.30
7 purchase totals =	$689.37		$735.0263	$735.03	$735.05	$735.10