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	$249.39	6.105%	$264.6153	$264.62	$264.60	$264.60
Purchase #2	$55.31	11.259%	$61.5374	$61.54	$61.55	$61.50
Purchase #3	$77.92	7.555%	$83.8069	$83.81	$83.80	$83.80
Purchase #4	$165.86	8.840%	$180.522	$180.52	$180.50	$180.50
Purchase #5	$181.42	10.151%	$199.8359	$199.84	$199.85	$199.80
Purchase #6	$213.54	4.549%	$223.2539	$223.25	$223.25	$223.30
Purchase #7	$66.40	13.360%	$75.271	$75.27	$75.25	$75.30
7 purchase totals =	$1,009.84		$1,088.8424	$1,088.85	$1,088.80	$1,088.80