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	$50.42	9.648%	$55.2845	$55.28	$55.30	$55.30
Purchase #2	$246.59	7.117%	$264.1398	$264.14	$264.15	$264.10
Purchase #3	$82.64	8.751%	$89.8718	$89.87	$89.85	$89.90
Purchase #4	$24.59	12.424%	$27.6451	$27.65	$27.65	$27.60
Purchase #5	$188.59	3.649%	$195.4716	$195.47	$195.45	$195.50
Purchase #6	$143.90	4.157%	$149.8819	$149.88	$149.90	$149.90
Purchase #7	$214.69	5.637%	$226.7921	$226.79	$226.80	$226.80
7 purchase totals =	$951.42		$1,009.0868	$1,009.08	$1,009.10	$1,009.10