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	$57.98	13.522%	$65.8201	$65.82	$65.80	$65.80
Purchase #2	$137.75	6.600%	$146.8415	$146.84	$146.85	$146.80
Purchase #3	$39.35	3.120%	$40.5777	$40.58	$40.60	$40.60
Purchase #4	$26.38	7.586%	$28.3812	$28.38	$28.40	$28.40
Purchase #5	$64.73	3.848%	$67.2208	$67.22	$67.20	$67.20
Purchase #6	$108.63	11.151%	$120.7433	$120.74	$120.75	$120.70
Purchase #7	$51.32	10.859%	$56.8928	$56.89	$56.90	$56.90
7 purchase totals =	$486.14		$526.4774	$526.47	$526.50	$526.40