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	$47.37	10.698%	$52.4376	$52.44	$52.45	$52.40
Purchase #2	$240.50	12.225%	$269.9011	$269.90	$269.90	$269.90
Purchase #3	$208.71	4.264%	$217.6094	$217.61	$217.60	$217.60
Purchase #4	$23.33	11.143%	$25.9297	$25.93	$25.95	$25.90
Purchase #5	$125.61	11.870%	$140.5199	$140.52	$140.50	$140.50
Purchase #6	$115.58	12.167%	$129.6426	$129.64	$129.65	$129.60
Purchase #7	$250.86	5.250%	$264.0302	$264.03	$264.05	$264.00
7 purchase totals =	$1,011.96		$1,100.0705	$1,100.07	$1,100.10	$1,099.90