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	$118.89	8.632%	$129.1526	$129.15	$129.15	$129.20
Purchase #2	$116.26	12.591%	$130.8983	$130.90	$130.90	$130.90
Purchase #3	$248.89	9.812%	$273.3111	$273.31	$273.30	$273.30
Purchase #4	$215.57	8.650%	$234.2168	$234.22	$234.20	$234.20
Purchase #5	$40.40	12.714%	$45.5365	$45.54	$45.55	$45.50
Purchase #6	$172.27	4.152%	$179.4227	$179.42	$179.40	$179.40
Purchase #7	$233.40	12.558%	$262.7104	$262.71	$262.70	$262.70
7 purchase totals =	$1,145.68		$1,255.2484	$1,255.25	$1,255.20	$1,255.20