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	$242.93	6.228%	$258.0597	$258.06	$258.05	$258.10
Purchase #2	$223.65	12.387%	$251.3535	$251.35	$251.35	$251.40
Purchase #3	$58.51	10.279%	$64.5242	$64.52	$64.50	$64.50
Purchase #4	$166.50	13.235%	$188.5363	$188.54	$188.55	$188.50
Purchase #5	$52.46	13.109%	$59.337	$59.34	$59.35	$59.30
Purchase #6	$89.82	11.383%	$100.0442	$100.04	$100.05	$100.00
Purchase #7	$65.97	5.777%	$69.7811	$69.78	$69.80	$69.80
7 purchase totals =	$899.84		$991.6360	$991.63	$991.65	$991.60