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	$39.78	7.622%	$42.812	$42.81	$42.80	$42.80
Purchase #2	$89.71	8.184%	$97.0519	$97.05	$97.05	$97.10
Purchase #3	$58.73	7.290%	$63.0114	$63.01	$63.00	$63.00
Purchase #4	$75.52	8.685%	$82.0789	$82.08	$82.10	$82.10
Purchase #5	$218.61	12.429%	$245.781	$245.78	$245.80	$245.80
Purchase #6	$154.53	7.791%	$166.5694	$166.57	$166.55	$166.60
Purchase #7	$87.30	3.638%	$90.476	$90.48	$90.50	$90.50
7 purchase totals =	$724.18		$787.7806	$787.78	$787.80	$787.90