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	$26.29	5.718%	$27.7933	$27.79	$27.80	$27.80
Purchase #2	$190.93	4.412%	$199.3538	$199.35	$199.35	$199.40
Purchase #3	$43.61	5.601%	$46.0526	$46.05	$46.05	$46.10
Purchase #4	$127.27	8.139%	$137.6285	$137.63	$137.65	$137.60
Purchase #5	$234.98	6.492%	$250.2349	$250.23	$250.25	$250.20
Purchase #6	$242.76	12.483%	$273.0637	$273.06	$273.05	$273.10
Purchase #7	$250.34	6.298%	$266.1064	$266.11	$266.10	$266.10
7 purchase totals =	$1,116.18		$1,200.2332	$1,200.22	$1,200.25	$1,200.30