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	$6.59	7.412%	$7.0785	$7.08	$7.10	$7.10
Purchase #2	$57.84	9.659%	$63.4268	$63.43	$63.45	$63.40
Purchase #3	$27.88	4.317%	$29.0836	$29.08	$29.10	$29.10
Purchase #4	$141.73	7.663%	$152.5908	$152.59	$152.60	$152.60
Purchase #5	$55.34	6.608%	$58.9969	$59.00	$59.00	$59.00
Purchase #6	$227.28	4.866%	$238.3394	$238.34	$238.35	$238.30
Purchase #7	$136.37	13.497%	$154.7759	$154.78	$154.80	$154.80
7 purchase totals =	$653.03		$704.2919	$704.30	$704.40	$704.30