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	$227.63	12.111%	$255.1983	$255.20	$255.20	$255.20
Purchase #2	$197.59	12.574%	$222.435	$222.44	$222.45	$222.40
Purchase #3	$83.28	5.365%	$87.748	$87.75	$87.75	$87.70
Purchase #4	$127.98	13.560%	$145.3341	$145.33	$145.35	$145.30
Purchase #5	$130.69	13.665%	$148.5488	$148.55	$148.55	$148.50
Purchase #6	$90.83	7.280%	$97.4424	$97.44	$97.45	$97.40
Purchase #7	$117.69	5.642%	$124.3301	$124.33	$124.35	$124.30
7 purchase totals =	$975.69		$1,081.0367	$1,081.04	$1,081.10	$1,080.80