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	$238.92	12.418%	$268.5891	$268.59	$268.60	$268.60
Purchase #2	$104.60	4.395%	$109.1972	$109.20	$109.20	$109.20
Purchase #3	$189.40	7.424%	$203.4611	$203.46	$203.45	$203.50
Purchase #4	$80.78	3.474%	$83.5863	$83.59	$83.60	$83.60
Purchase #5	$102.59	11.695%	$114.5879	$114.59	$114.60	$114.60
Purchase #6	$173.68	3.194%	$179.2273	$179.23	$179.25	$179.20
Purchase #7	$137.96	12.868%	$155.7127	$155.71	$155.70	$155.70
7 purchase totals =	$1,027.93		$1,114.3616	$1,114.37	$1,114.40	$1,114.40