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	$246.28	6.547%	$262.404	$262.40	$262.40	$262.40
Purchase #2	$103.79	5.827%	$109.8378	$109.84	$109.85	$109.80
Purchase #3	$77.67	3.707%	$80.5492	$80.55	$80.55	$80.50
Purchase #4	$178.88	11.476%	$199.4083	$199.41	$199.40	$199.40
Purchase #5	$233.48	12.842%	$263.4635	$263.46	$263.45	$263.50
Purchase #6	$228.52	12.247%	$256.5068	$256.51	$256.50	$256.50
Purchase #7	$193.29	3.108%	$199.2975	$199.30	$199.30	$199.30
7 purchase totals =	$1,261.91		$1,371.4671	$1,371.47	$1,371.45	$1,371.40