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	$166.83	9.374%	$182.4686	$182.47	$182.45	$182.50
Purchase #2	$121.76	5.745%	$128.7551	$128.76	$128.75	$128.80
Purchase #3	$243.30	8.629%	$264.2944	$264.29	$264.30	$264.30
Purchase #4	$59.42	3.291%	$61.3755	$61.38	$61.40	$61.40
Purchase #5	$60.92	4.316%	$63.5493	$63.55	$63.55	$63.50
Purchase #6	$139.42	3.272%	$143.9818	$143.98	$144.00	$144.00
Purchase #7	$139.91	6.774%	$149.3875	$149.39	$149.40	$149.40
7 purchase totals =	$931.56		$993.8122	$993.82	$993.85	$993.90