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	$42.89	12.661%	$48.3203	$48.32	$48.30	$48.30
Purchase #2	$62.92	4.793%	$65.9358	$65.94	$65.95	$65.90
Purchase #3	$108.78	13.238%	$123.1803	$123.18	$123.20	$123.20
Purchase #4	$137.87	10.578%	$152.4539	$152.45	$152.45	$152.50
Purchase #5	$126.84	6.701%	$135.3395	$135.34	$135.35	$135.30
Purchase #6	$129.48	13.236%	$146.618	$146.62	$146.60	$146.60
Purchase #7	$69.89	3.765%	$72.5214	$72.52	$72.50	$72.50
7 purchase totals =	$678.67		$744.3692	$744.37	$744.35	$744.30