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	$152.56	10.251%	$168.1989	$168.20	$168.20	$168.20
Purchase #2	$117.39	9.531%	$128.5784	$128.58	$128.60	$128.60
Purchase #3	$238.45	4.356%	$248.8369	$248.84	$248.85	$248.80
Purchase #4	$224.33	7.248%	$240.5894	$240.59	$240.60	$240.60
Purchase #5	$109.96	3.755%	$114.089	$114.09	$114.10	$114.10
Purchase #6	$20.52	4.673%	$21.4789	$21.48	$21.50	$21.50
Purchase #7	$158.42	6.737%	$169.0928	$169.09	$169.10	$169.10
7 purchase totals =	$1,021.63		$1,090.8643	$1,090.87	$1,090.95	$1,090.90