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	$61.53	11.556%	$68.6404	$68.64	$68.65	$68.60
Purchase #2	$118.56	8.645%	$128.8095	$128.81	$128.80	$128.80
Purchase #3	$113.27	12.760%	$127.7233	$127.72	$127.70	$127.70
Purchase #4	$186.47	13.164%	$211.0169	$211.02	$211.00	$211.00
Purchase #5	$52.65	3.392%	$54.4359	$54.44	$54.45	$54.40
Purchase #6	$39.58	4.304%	$41.2835	$41.28	$41.30	$41.30
Purchase #7	$249.73	12.455%	$280.8339	$280.83	$280.85	$280.80
7 purchase totals =	$821.79		$912.7434	$912.74	$912.75	$912.60