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	$159.31	4.479%	$166.4455	$166.45	$166.45	$166.40
Purchase #2	$243.92	7.754%	$262.8336	$262.83	$262.85	$262.80
Purchase #3	$102.69	8.841%	$111.7688	$111.77	$111.75	$111.80
Purchase #4	$150.29	11.800%	$168.0242	$168.02	$168.00	$168.00
Purchase #5	$190.38	13.870%	$216.7857	$216.79	$216.80	$216.80
Purchase #6	$196.64	5.318%	$207.0973	$207.10	$207.10	$207.10
Purchase #7	$5.61	11.712%	$6.267	$6.27	$6.25	$6.30
7 purchase totals =	$1,048.84		$1,139.2221	$1,139.23	$1,139.20	$1,139.20