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	$110.43	11.376%	$122.9925	$122.99	$123.00	$123.00
Purchase #2	$42.34	8.499%	$45.9385	$45.94	$45.95	$45.90
Purchase #3	$30.31	13.209%	$34.3136	$34.31	$34.30	$34.30
Purchase #4	$48.37	4.420%	$50.508	$50.51	$50.50	$50.50
Purchase #5	$103.48	5.818%	$109.5005	$109.50	$109.50	$109.50
Purchase #6	$141.28	8.334%	$153.0543	$153.05	$153.05	$153.10
Purchase #7	$63.42	12.852%	$71.5707	$71.57	$71.55	$71.60
7 purchase totals =	$539.63		$587.8781	$587.87	$587.85	$587.90