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	$235.50	13.213%	$266.6166	$266.62	$266.60	$266.60
Purchase #2	$241.59	3.722%	$250.582	$250.58	$250.60	$250.60
Purchase #3	$171.95	3.822%	$178.5219	$178.52	$178.50	$178.50
Purchase #4	$144.58	5.570%	$152.6331	$152.63	$152.65	$152.60
Purchase #5	$82.79	5.818%	$87.6067	$87.61	$87.60	$87.60
Purchase #6	$91.65	8.506%	$99.4457	$99.45	$99.45	$99.40
Purchase #7	$17.31	4.170%	$18.0318	$18.03	$18.05	$18.00
7 purchase totals =	$985.37		$1,053.4378	$1,053.44	$1,053.45	$1,053.30