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	$80.70	11.140%	$89.69	$89.69	$89.70	$89.70
Purchase #2	$237.66	11.616%	$265.2666	$265.27	$265.25	$265.30
Purchase #3	$50.34	11.403%	$56.0803	$56.08	$56.10	$56.10
Purchase #4	$93.56	6.737%	$99.8631	$99.86	$99.85	$99.90
Purchase #5	$197.65	12.686%	$222.7239	$222.72	$222.70	$222.70
Purchase #6	$189.87	11.442%	$211.5949	$211.59	$211.60	$211.60
Purchase #7	$233.59	12.188%	$262.0599	$262.06	$262.05	$262.10
7 purchase totals =	$1,083.37		$1,207.2787	$1,207.27	$1,207.25	$1,207.40