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	$101.56	6.642%	$108.3056	$108.31	$108.30	$108.30
Purchase #2	$115.67	10.754%	$128.1092	$128.11	$128.10	$128.10
Purchase #3	$200.81	10.314%	$221.5215	$221.52	$221.50	$221.50
Purchase #4	$68.27	9.550%	$74.7898	$74.79	$74.80	$74.80
Purchase #5	$231.86	11.300%	$258.0602	$258.06	$258.05	$258.10
Purchase #6	$141.77	10.642%	$156.8572	$156.86	$156.85	$156.90
Purchase #7	$160.76	11.525%	$179.2876	$179.29	$179.30	$179.30
7 purchase totals =	$1,020.70		$1,126.9311	$1,126.94	$1,126.90	$1,127.00