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	$222.60	10.668%	$246.347	$246.35	$246.35	$246.30
Purchase #2	$166.96	7.454%	$179.4052	$179.41	$179.40	$179.40
Purchase #3	$180.91	6.164%	$192.0613	$192.06	$192.05	$192.10
Purchase #4	$164.78	12.456%	$185.305	$185.31	$185.30	$185.30
Purchase #5	$115.93	9.562%	$127.0152	$127.02	$127.00	$127.00
Purchase #6	$15.91	9.808%	$17.4705	$17.47	$17.45	$17.50
Purchase #7	$133.88	7.349%	$143.7188	$143.72	$143.70	$143.70
7 purchase totals =	$1,000.97		$1,091.3230	$1,091.34	$1,091.25	$1,091.30