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	$127.87	13.503%	$145.1363	$145.14	$145.15	$145.10
Purchase #2	$29.83	4.533%	$31.1822	$31.18	$31.20	$31.20
Purchase #3	$135.78	13.349%	$153.9053	$153.91	$153.90	$153.90
Purchase #4	$91.96	8.660%	$99.9237	$99.92	$99.90	$99.90
Purchase #5	$122.84	7.127%	$131.5948	$131.59	$131.60	$131.60
Purchase #6	$61.90	9.480%	$67.7681	$67.77	$67.75	$67.80
Purchase #7	$218.41	5.216%	$229.8023	$229.80	$229.80	$229.80
7 purchase totals =	$788.59		$859.3127	$859.31	$859.30	$859.30