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	$225.38	11.768%	$251.9027	$251.90	$251.90	$251.90
Purchase #2	$122.50	7.277%	$131.4143	$131.41	$131.40	$131.40
Purchase #3	$211.45	10.571%	$233.8024	$233.80	$233.80	$233.80
Purchase #4	$91.87	11.476%	$102.413	$102.41	$102.40	$102.40
Purchase #5	$87.41	8.752%	$95.0601	$95.06	$95.05	$95.10
Purchase #6	$186.32	5.495%	$196.5583	$196.56	$196.55	$196.60
Purchase #7	$164.45	3.720%	$170.5675	$170.57	$170.55	$170.60
7 purchase totals =	$1,089.38		$1,181.7183	$1,181.71	$1,181.65	$1,181.80