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	$82.58	9.581%	$90.492	$90.49	$90.50	$90.50
Purchase #2	$150.93	4.582%	$157.8456	$157.85	$157.85	$157.80
Purchase #3	$187.39	6.833%	$200.1944	$200.19	$200.20	$200.20
Purchase #4	$16.59	13.447%	$18.8209	$18.82	$18.80	$18.80
Purchase #5	$132.61	4.220%	$138.2061	$138.21	$138.20	$138.20
Purchase #6	$27.70	6.196%	$29.4163	$29.42	$29.40	$29.40
Purchase #7	$69.59	4.247%	$72.5455	$72.55	$72.55	$72.50
7 purchase totals =	$667.39		$707.5208	$707.53	$707.50	$707.40