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	$40.46	6.605%	$43.1324	$43.13	$43.15	$43.10
Purchase #2	$231.51	7.141%	$248.0421	$248.04	$248.05	$248.00
Purchase #3	$208.27	4.739%	$218.1399	$218.14	$218.15	$218.10
Purchase #4	$222.97	11.781%	$249.2381	$249.24	$249.25	$249.20
Purchase #5	$45.27	11.174%	$50.3285	$50.33	$50.35	$50.30
Purchase #6	$32.47	11.298%	$36.1385	$36.14	$36.15	$36.10
Purchase #7	$75.64	8.597%	$82.1428	$82.14	$82.15	$82.10
7 purchase totals =	$856.59		$927.1623	$927.16	$927.25	$926.90