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	$62.52	9.248%	$68.3018	$68.30	$68.30	$68.30
Purchase #2	$31.37	3.653%	$32.5159	$32.52	$32.50	$32.50
Purchase #3	$124.96	7.504%	$134.337	$134.34	$134.35	$134.30
Purchase #4	$143.71	12.841%	$162.1638	$162.16	$162.15	$162.20
Purchase #5	$123.88	3.137%	$127.7661	$127.77	$127.75	$127.80
Purchase #6	$50.51	9.191%	$55.1524	$55.15	$55.15	$55.20
Purchase #7	$179.46	6.362%	$190.8772	$190.88	$190.90	$190.90
7 purchase totals =	$716.41		$771.1142	$771.12	$771.10	$771.20