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	$131.78	5.563%	$139.1109	$139.11	$139.10	$139.10
Purchase #2	$152.96	7.329%	$164.1704	$164.17	$164.15	$164.20
Purchase #3	$121.36	5.235%	$127.7132	$127.71	$127.70	$127.70
Purchase #4	$12.78	9.533%	$13.9983	$14.00	$14.00	$14.00
Purchase #5	$157.40	3.220%	$162.4683	$162.47	$162.45	$162.50
Purchase #6	$86.47	12.513%	$97.29	$97.29	$97.30	$97.30
Purchase #7	$130.29	11.256%	$144.9554	$144.96	$144.95	$145.00
7 purchase totals =	$793.04		$849.7065	$849.71	$849.65	$849.80