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	$27.60	5.566%	$29.1362	$29.14	$29.15	$29.10
Purchase #2	$7.57	5.440%	$7.9818	$7.98	$8.00	$8.00
Purchase #3	$240.83	5.159%	$253.2544	$253.25	$253.25	$253.30
Purchase #4	$88.63	11.582%	$98.8951	$98.90	$98.90	$98.90
Purchase #5	$149.69	6.107%	$158.8316	$158.83	$158.85	$158.80
Purchase #6	$137.32	10.798%	$152.1478	$152.15	$152.15	$152.10
Purchase #7	$12.72	7.111%	$13.6245	$13.62	$13.60	$13.60
7 purchase totals =	$664.36		$713.8714	$713.87	$713.90	$713.80