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	$184.78	12.474%	$207.8295	$207.83	$207.85	$207.80
Purchase #2	$59.83	10.125%	$65.8878	$65.89	$65.90	$65.90
Purchase #3	$235.54	10.157%	$259.4638	$259.46	$259.45	$259.50
Purchase #4	$52.80	4.438%	$55.1433	$55.14	$55.15	$55.10
Purchase #5	$250.54	5.608%	$264.5903	$264.59	$264.60	$264.60
Purchase #6	$246.34	11.503%	$274.6765	$274.68	$274.70	$274.70
Purchase #7	$86.96	9.152%	$94.9186	$94.92	$94.90	$94.90
7 purchase totals =	$1,116.79		$1,222.5098	$1,222.51	$1,222.55	$1,222.50