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	$46.53	9.774%	$51.0778	$51.08	$51.10	$51.10
Purchase #2	$137.76	12.303%	$154.7086	$154.71	$154.70	$154.70
Purchase #3	$141.87	4.713%	$148.5563	$148.56	$148.55	$148.60
Purchase #4	$9.46	12.102%	$10.6048	$10.60	$10.60	$10.60
Purchase #5	$92.76	11.615%	$103.5341	$103.53	$103.55	$103.50
Purchase #6	$55.69	3.841%	$57.8291	$57.83	$57.85	$57.80
Purchase #7	$35.28	7.573%	$37.9518	$37.95	$37.95	$38.00
7 purchase totals =	$519.35		$564.2625	$564.26	$564.30	$564.30