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	$28.37	10.636%	$31.3874	$31.39	$31.40	$31.40
Purchase #2	$164.74	6.343%	$175.1895	$175.19	$175.20	$175.20
Purchase #3	$219.56	3.602%	$227.4686	$227.47	$227.45	$227.50
Purchase #4	$60.90	5.592%	$64.3055	$64.31	$64.30	$64.30
Purchase #5	$185.96	5.656%	$196.4779	$196.48	$196.50	$196.50
Purchase #6	$21.90	7.746%	$23.5964	$23.60	$23.60	$23.60
Purchase #7	$137.80	10.325%	$152.0279	$152.03	$152.05	$152.00
7 purchase totals =	$819.23		$870.4532	$870.47	$870.50	$870.50